A partially fill die can make the devices shallow. Some devices can be reduced in size when dies are over polished. The letters are tapered. Wide at the bottom and narrower at the top. If you consider the two images, the upper you are only considering the upper part of the device when you are looking at it. The lower is considering the lower part of the device. The two images are the same size at the base. so that is what you are seeing. A partially filled die with a little grease making the ones' device appear shorter.
Richard S. Cooper
Some have asked about my images I use and I've glad to say I've completed a DVD of these. Ask if you are interested.