Motion5 - Size of DropZone

This may seem like a ridiculous question but, please forgive; I am new to Motion.

In the drop zone box below, which part of it does my image actually fit in? Is it only the white box surrounding the arrow in the center or is it the entire white + gray area, i.e. the total gray area from the left edge of the gray box to the end of it on the right.

I am trying to gauge the size of it because I have an image on the left and one on the right and I don't want them to collide.