Amwa, oddly enough I am the other way. Governed by numbers as opposed to my body, I no longer have any knowledge of what constitutes a normal human portion either.
I know that a meal should be between 350g and 450g for an average adult. But that's a number. I don't know what it really IS.
I know how many calories are in everything and for each meal, have a set "number." It's sad because I place quotation marks around it for a reason; because foods are numbers to me. So I'll say, "I'm having a 230 and a 210 and a 45, so that's about 500 kcal". I add stuff up that way, and whether or not it's an ENORMOUS, BELLY HURTING pile of food or a morsel of nibblage, that's what I'll eat.
It's weird because I have a great appetite too, but when it comes to numbers, I rarely deviate. If I've not had my specific numbers but my stomach aches with being full, I still plough on and eat my numbers. If I am hungry but I've made up my numbers, I won't eat.
You're in an enviable position to be able to answer your body's call, and I say, to an extent, go with it!!