I didn't understand why you kept saying you couldn't see "where" it curved (by which I assume you mean drop or hop), then I looked at these charts and realize you probably can't see the hop created due to the bb's characteristic at your low muzzle energy.
When I adjust my hop, I just look for that little hump or hop that occurs just around the point when the bb starts to drop dramatically. I'm not really looking at "where" it's happening, but rather I'm looking to see if that hump or hop exists. (Look at the green line.)
I would first do what everyone else says and improve your fps first, then go from there.