Min pay on reserve is 75 hours per month. There's no min day pay on reserve there's a difference there.
Each day is valued at 3.9 hours but it's not a min day. Only matters if you can get a drop, vacation, sick, or training.

You won't break guarantee on reserve, so "4 days for 2 hours of pay" isn't a concern for reserves.

While on reserve I had a two day 12 hour trip followed next sequence by a five day 10 hour trip. Awful tough to break guarantee on reserve like that. And as pointed out, no daily guarantee, just the 75 for the month. You can bust your butt for a couple days, but a few slow days makes it all for naught.

Right... but for trips. As a line holder its common to have lost days and inefficient trips that are 4 days away from home for 9 hours pay.

Eh. I wouldn’t say “common” for a 9 hour four day on a line. That would require all the other trips to be 16 plus hours and that would be a 19 day, 72 hour line. While I agree many lines are certainly not very good, most are not that bad.

That's reserve pretty much anywhere. Unless the airline is disastrously understaffed, which brings other QOL issues.
Thankfully we have rules that prevent the worst abuse of reserves.

Not common at all. Actually, almost unheard of.
Some 7-10 hour 3 day-trips (which you can most of the time trade away from to a much more productive 4-day), but the 7-9 hour 4-days in open time are scraps from trips where people pick up the turns from the first or last day.

That's the point min day pay would be every day on reserve is 3.9 hours so if you flew anything beyond 3.9 hours it would be above guarantee. So no min day pay just monthly guarantee.

Reserve is 75 hours 12 days off. You want to break guarantee on reserve not going to happen unless you pick up open time of your days off. Open time is on top of guarantee pay.

11, not 12.