HI! I have had the exact same problem. I do find that if I drink larger quantities of water, peeing without emptying my pouch becomes easier.
I am 8 months post take-down and when my pouch is off (as if I was in a UC flare, straining horribly, spending too much time on the toilet, etc) peeing is very difficult. When the straining is at it's worse, peeing is almost impossible. It eventually becomes normal again but it can take a while.
Best of luck!!!!