Try imagine a jump in front of you all the time, now imagine your foots sole purpose pointing at the jump . Your leg will be calmer and as a nice side effect your heel will come a little bit lower.
Hope this helps...
Yes , put a piece of paper or a coin between ur lower leg and the horse, and ride without letting it fall, that will make u get the presure on the correct place :)
There any other exercise that can help?
Generally the cause is a exesive pressure of the knees on the saddle , no strirrups work should help ;)