Easy rule, when ramping regardless of the number of target reps (1,2 or 3RM) the ramp should last between 8-12 sets from the first loaded set which you start at 50-60%.
So you basically have 8-12 sets to go from 50-60% to 90-100% (depending of if you are using a 1, 2 or 3RM).
Just go with some logic...
If your best on a lift is 165lbs then you must cover about 80lbs in 8-12 sets... can you do 20lbs jumps? No!.. Jumps of 10 at the start then finishing with jumps of 5 would be better.
If your best on a lift is 225lbs then you must cover about 110lbs in 8-12 sets. Jumps of 10lbs will get you there in 11 sets, so that's fine
If your best on a lift is 350lbs then you must cover roughly 170-180lbs in 8-12 sets... jumps of 20lbs should get you there in about 8 or 9 sets, so you can start out at 20lbs and even switch to 10lbs jumps at the end of the ramp.
If your best on a lift is 500lbs you must cover 250lbs in 8-12 sets so jumps of 20lbs might not even be enough, you might want to go with 30lbs jumps which will get you there in 8 sets... or start out at 30 and switch to 20 at the end of the ramp.