They aren't dead over knot or two IMO, they are dead due to lack of correlation between pitch, airspeed, control placements, and power. They don't understand what the airplane is doing outside and how that relates to the control positions inside. I'd say trim never comes into it significantly. If if did, the FAA and manufacturer would say something like "Warning! Use of trim can adversely affect Vmc and Aircraft Control! Do not use trim!!" (lol).
It's trying to make something out of nothing. It's like asking "what affects takeoff distance" and having to talk about how round the tires are, their coefficient of friction depending on the temperature, how the cabin air vent(s) might be open and increasing drag due to ram pressure as the air tends to "pile up" outside an open vent, etc. Discussing those things indicates a lack of understanding about the real subjects and the time should be spent ensuring those are understood and delving into more significant topics. Lord knows there's never enough time to cover the important stuff and spend time really assessing and discussing it. The more a student got experience DISCUSSING and EXPLAINING the relevant factors was usually better, because they could usually use the practice at not getting tripped up while explaining critical engine asymmetrical p-factor, accelerated slipstream, how torque effects, etc.
The point I was trying to make initially is this "8 (9) factors of Vmc" thing came directly from 23.149 and it's been a rote-answer thing for so long that people don't even know what they are talking about anymore, students, DPEs, and everyone in between. They don't know how the "factors" apply or what they are about (worst-case scenario conditions and setup for an engine failure, not "things that affect Vmc").
§ 23.149 Minimum control speed.
(a) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees. The method used to simulate critical engine failure must represent the most critical mode of powerplant failure expected in service with respect to controllability.
(b) VMC for takeoff must not exceed 1.2 VS1 , where VS1 is determined at the maximum takeoff weight. VMC must be determined with the most unfavorable weight and center of gravity position and with the airplane airborne and the ground effect negligible, for the takeoff configuration(s) with—
(1) Maximum available takeoff power initially on each engine;
(2) The airplane trimmed for takeoff;
(3) Flaps in the takeoff position(s);
(4) Landing gear retracted; and
(5) All propeller controls in the recommended takeoff position throughout.
To the list of things that really affect control and may change on any given day/conditions/flight that you can extrapolate from above I'd add:
Control placement and zeroSS vs zeroYaw, which engine failed and how fast you are going.
The PTS really tells the tale. I'll include my own "drill down" for what I'd probably ask during a checkride:
1. meaning of the term “critical engine.”
What factors determine what the critical engine is?
Which one is it?
Why?
Would the extent of these be the same in cruise compared to climbout?
Do all ME planes have a critical engine?
2. effects of density altitude on the VMC demonstration.
How does DA affect Vmc?
If you were at very high density altitude, would you expect to stall first or lose control first? Why?
Would your control inputs be the same, less or more and why?
If this covered number 5, then I'd skip 5.
3. effects of airplane weight and center of gravity on control.
What are some effects of weight on control? (as long as there are two thrown out that are correct, that's usually passing for me, 3-4 is outstanding if possible, these also could oppose each other, which is fine).
How would an aft CG affect control?
What about a forward one?
Why?
4. effects of angle of bank on VMC.
What would be the effect on Vmc if I banked more into the operative engine than 5 degrees?
Is there any negative to doing that?
What if I decided to just keep the wings level and only use rudder to stop yaw?
If the applicant is very good, he may cover anything I'd ask in number 8, so depending on the answers here I may skip 8.
5. relationship of VMC to stall speed.
May have already been covered, but I'd ask about this, the most dangerous situation and why, what we'd expect in OUR airplane based on ITs numbers and performance, and maybe a few comparisons like turbocharged.
6. reasons for loss of directional control.
Why do we yaw and roll when we have an engine failure? (you'd think it's easy, but most people think way too much into it)
7. indications of loss of directional control.
How would you know you are losing directional control or having an engine failure?
8. importance of maintaining the proper pitch and bank
attitude, and the proper coordination of controls.
What control inputs do we want to use to control the airplane while SE?
Why?
Do they change depending on the situation?
What pitch attitude would we fly?
What airspeed?
Why?
Would you fly at any other airspeed?
9. loss of directional control recovery procedure.
If you start to lose directional control, how do you recover?
This could also be asking what are the steps you take if your engine fails?
10. engine failure during takeoff including planning, decisions,
and single-engine operations.
Would ask about decision to continue vs abort.
What is accel-stop vs accel-go.
Calculating SE performance or what to expect.
Factors that affect SE decision planning and under what circumstances decisions are different, failures right after takeoff, etc.
(and yes, I have nothing better to do tonight).