I am an After Effects newbie (have been using Premier Pro CS5 for a few years - but by no means know all its possabilities).
When I use after effcts compositions in Prem Pro using the Adobe Dynamic Link, all the compositions need to be reduced by 50% to fit on the screen. This gets a pain constantly having to reduce the size for every clip.
Have played with composition settings, but that just seems to crop the image.
Suspect it is something basic, but cant find out what it is. Timelines are set at 720 x 576 (DV PAL Widescreen)
Your After Effects comps should match the size of your sequence settings in Premiere Pro. If the footage in Premiere Pro does not match the sequence size and you have scaled the footage to match AE should see the scale factors.
Where are you reducing the size to 50%? If it is in the comp window then that may be normal. The comp window is just a viewer just as the viewer in Premiere Pro does not represent the full sized image. What you are seeing may be completely normal.
If, on the other hand, you are having to go into the composition settings and adjust the frame size of the composition we need to know a lot more about your project and see some screenshots.