On your original design "Sepulcher" i have a few ideas, but again, first i have to acknowledge that we all have different styles and philosophies to approach mecha design. So here are just my own thoughts, neither correct nor wrong...
The head seems heavily influenced by the gundam GM design, which appears blocky, unlike the FSS mech skull, which looks more pointy at the chin and almost always "hidden" under a big crown-like hood.
gundam GM
The hand is very small, and somewhat bears the look (and feel) of Mr. Gpenguin's hallmark designs (i.e. tiny hands, tiny feet)...
A big feature of Mr. Nagano's design is that he uses a lot of long fluid curves in fabricating the structures, which are not very present in your designs. It's interesting that you seem to prefer short, straight, hard lines to soft curves. This seems to be your style.