(for mine) it's a mech that uses primarily synthetic muscles for movement instead of motors and hydraulics. With the pilot "jacking in" movement is much more human and so they are much more capable in close quarters urban combat. They are expensive and require the pilot undergo surgery, so they're rare.
For this one, near the back below the shoulders, to protect the pilot from heavy frontal hits. In general the designs place the pilot central or rear. I'm also undecided if the cockpit will be a gel filled "plug" or just a tight conventional one. As pilot movement is minimal, most control working through the neural link. May have the cockpit style change depending on faction and the mechs tech level.