Not quite sure how to answer your question but will give it a try. There is about 1/2" room between the bottom of the carriage and the mat. We have had users take their cell phones and engrave the backs of them (on the cover) for instance. So your material has to be thin enough to fit under the carriage. Is that what you mean? You can go to
www.silverbulletcutters.com and see examples of engraving on a variety of projects.
As far as leather goes, it IS about density because there are some leathers that emboss/engrave better than others because of their density - just like there are some that cut better and it's about the material, not necessarily the height.
I would also encourage you to browse through the Masterpieces Section to see a variety of projects. We are not all up to date with posting photos, but if there is something in particular you want to see and cannot find, please ask.
You might want to talk directly with Sherri if you have not already done so. She will be able to clearly address any and all of your concerns.