As far as I know, cats do not use their whiskers to detect the food, they go with smell sense, and some say that whiskers are almost a problem with food in deep dishes.Maybe this is an odd question, and perhaps I should have asked it before - the vet shaved his whiskers off due to where the surgery was, and they haven't grown back yet - could that be affecting his ability to "find" the bits of food in his bowl? Although I say bowl, it's actually fairly flat, more of a small plate that we have always used to give him food.
Nevertheless I think that the diminished perception of the world around him, especially if it's asymmetrical, might bother him to the point that he feels not quite right, I don't know...
My cat Lola lost all her whiskers due to the radiation therapy she received on her face to treat the cancer she had into he rnose, but she didn't show any trouble. They grew back some months later and were a bit shorter, more fragile and some of them were twisted, crimpled.
But, again, every cat is different.