Well, GV to GV may be different. I have heard historical accounts of tigers sustaining 200+ shots from russian tanks at close range and still making it home. But I know exactly what you mean, I've gone tiger vs. tiger, hit the guy in the rear 20+ times, popped his engine on the first shot, but the following shots seemed to do nothing. I probably could've unloaded everything into him and he would still be sitting there if he hadn't got ganged by some panzers heading out to his spawn point. Food for thought, I will say that reevaluation of the GV model may not be a bad idea if there were time.
--Howitzer