right click on the frame: check out the fitting options.
How do we keep the same scale size when updating or relinking images in CS 5? In the preferences we already have Preserve Image Dimensions when Linking checked. When we relink the object seems to fit to box.
If you want to preserve the SCALE, not the size of the image in the frame, UNCHECK that option. The purpose for that is to keep the image from changing size when you change the resolution without resampling.