Hi - to answer your question, lots of ways to lower how much listed above. I have both a replaced hip and a replaced knee, and we looked at angles quite a bit. On a TT 'Rover' with 152mm cranks, my knee flexes to 73 degrees, and my hip closes to 90 degrees. Shorter cranks would indeed lower both of these numbers even more.

Also, look at the BB height in relation to the seat height - this will affect hips more than knees (but sometimes one follows the other).

Another possible note? Unless you have actual damage, going into PT *could* be a way to gain more flex?? When a person gets a TKR, they lose flex in both directions, and weeks/months of PT may be required to bring it back (this assumes the joint is capable of the motion. Lastly, have you thought to see an Ortho about this issue?