Trouble with bounding boxes

Hi all!
I'm trying to export a helmet FBX from 3ds max on to a character model I already have in unity.
The character already has a bounding box around his head where the helmet should be if I selected my helmet's mesh into the Skinned Mesh Renderer, but when I do, the helmet it appears in his chest and it's only half the size it should be!
I've gone back into 3ds max to check if the helmet's origin point is right, rotation, size ... everything seems to be fine.
I have no idea what's going on. Please help.
I'm no good at communicating ideas so, please click on the attachments to see what I'm trying to say.

Thanks!!