yep…track matte key in Premiere is not very good. In the old Final Cut 7 you could place your matte where you want it and move and re-size your fill footage with ease. this is what i do…place your matte where you want it to be then nest it. put your footage below the matte nest then nest the footage. so you will have 2 nests now. open the footage nest and apply the matte nest above it. make the matte nest 50% transparent to act as a guide. re-size and move your footage to fill the transparent nest. when you get the footage the way you want it then disable the matte nest.
there you go…done the hard way.