I would not call 3 oz a small meal. 1.5 oz, yes I'd call that a small meal.
Wondering where you come up with the 4 cans of FF (Fancy Feast) or 12 ounces of food a day?
Does he not want to eat more than 3 oz of food at a time?
Would you say his current weight is his ideal weight? (for most cats it's around 10-12 pounds)
You've probably seen a chart like this at your vet's office, for assessing a cat's weight and condition
ECID. (Every Cat is Different) When my Wink first came into my home, he would eat up to 12 ounces a day. But that amount of food gradually reduced to about 5.5 to 6.5 ounces a day. He was still unregulated in the beginning so was always starving. He lost weight on the canned food diet during the first couple of months (a bit too fast of a weight loss) so then he gained some back over the subsequent couple of months when he went into remission.
Your cat may need more or less food to maintain weight. If Simba is too thin, then a bit more food for a while would be good. If he starts to gain too much weight, less food. Good idea to check his weight once a week at home. You probably have a scale at home, so hold him in your arms, step on the scale, note number, let Simba get down, and see what your weight is. Subtract to get difference. Not as precise as the scale at the vets office, but close enough to see a general trend. It's what I do with my CKD kitty.
After remission, I wanted to keep a close eye on his food intake and weight, so I developed and kept a spreadsheet for each month to track him on an ongoing basis. Wanted to never have the neuropathy happen again, as that is so, so painful. Find what works for you.