People who have seen Marsters up close and personal say he's about 5'8". Look at the power walk shots and you'll see he's quite short. In the scenes where he talking to Christian Kane, he's only a little taller than CK and CK is only about 5'7" (there's a reason he's called little lawyer Lindsey.)

How does JM only appear to be a little bit shorter than DB? Easy - he's on a box. (Look at SMG and DB - she would have come up to his belly button if she hadn't been on a box half the time.)