Gunter actually has some muscle and unlike others (Dillet rings a bell) Gunter could very well just be missing the drug variable. It's clear he is in good shape just small.
That's drugs.
Drugs are just the finishing touches.
I'm going to agree with Rocco, Gunther in his prime was a HUGE man. He seemed taller than 6 though.
Prime Ronnie was the most impressive, even in shorts and a t shirt he looked like he was from another planet. Cutler was unusually wide, Priest had arms that were unreal and Kovacs was a sweaty pig.