Capacity does indeed diminish quickly. Even more so for the curl function. Since the distance between the bucket pivot, and where the cylinder attaches is a relatively short distance compared to where the lift cylinder attaches vs the loader arm pivot.
At the tip of a 4' fork, I would guess the curl function to be weaker than the lift. Even know the rollback force is about double what the lift force is rated at.
Given you had 650# out there a ways, and 2200psi is a tad on the light side IMO, I dont think you have anything wrong. I would be looking at shimming your PRV though. Get that thing up to at least 2400psi. Mine has been running several years now at 2650 with no issues at all. But the added lift is indeed noticeable.