I'm having difficulty seeing anything wrong with the images you posted. Perhaps I don't understand your intended point of focus.

Isn't the Pentax an APS-C sensor? If it is, that sensor produces an inherently greater DOF over a FX sensor at a given focal length and lens to subject distance. Could it be that you are used to the look of the deeper DOF?

I think you would have a better shot at a critical evaluation of the focus system (e.g. chosen point of focus and actual point of focus) using a flatter target. First test is can it produce an accurately focused image on a flat target. If not then investigate the actual depth. Do all this before you try any adjustment. It's quite a trick evaluation.

Roger
It's still, ISO, aperture and shutter-speed, right?