Its very very individual… I have 9cm drop, which allows me to ride in the hoods with 90 degrees bent arms (which is most aero), so for me that works well.
But I see a lot of riders who push crazy drops because it looks cool, and they ride with locked arms to just reach the hoods, which is idiotic.
There is a difference between flats and climbs when it comes to hips, reach and all other factors, so it might be that you get some sort of hip impingement when you are climbing…
Have you had a proper bike fit?
I would try to raise the front a bit and see how that feels 