Originally Posted by fosters

It'll actually be around 40 miles (try it, I promise), and it's the way you're supposed to do it to get an accurate depiction of what you are painting. Because of the size of the RJ's RADAR 40-45 miles is the limit of it correctly picking up returns at altitude. Larger domes can go out 80 miles or so.

If you still don't believe me, look to an expert - David Gwinn. Gwinn's stuff is actually on Sporty's.

How Radar Works (Booklet and Audio CD) - Sporty's Pilot Shop

I've flown with 30+ year CA's who thought the RADAR was connected to the plane and when titled up +10 on departure was really tilted +25 because of the deck angle on the plane. Just because you've flown 8000 hours doesn't mean you don't know how to use the RADAR (don't worry, most don't).

Your way works OK for en route avoidance when you have a lot of space to go around cells. But it's not the most accurate way to do it.