you have the normal aikido uke mentality, i.e. attack then waiting for things to be done on you. you should lead. get your feet under your center as much as you can. also, think of kaeshi waza every time you do ukemi. don't have to carry it out, but be in the position that you could. there is a teacher in my organization, Dan Messisco. he got a very interesting take on ukemi, a sample of his stuffs http://www.youtube.com/watch?v=yBe7dQDT9mo
. watch his body posture when he took ukemi.
btw, i liked your teacher's stuffs.