I know this isn't going to happen because I'm not from Japan GH doesn't care about feedback/our ideas, but I had a pretty sweet idea for it all the same. Every time you feed, one slot would be a chosen as the skill up slot. If the skill up material is in that slot, you would get a skill up. This means that if you feed 5 of the same skill up, you would be guaranteed one skill up.

When the rate goes up, there would be more slots chosen. So 2x would be 2 slots chosen of the 5, 3 slots would be 3, 5 would mean 100% skill up rate. The expected value would always be the same so there would never be a 'best number to feed', but the gamble would change drastically- if you feed 2 on 1x rates separately, you would have a .64 chance of no skill ups, .04 chance of two skill ups, and a .32 chance of 1 skill up, but if you fed both at once you would have a .6 chance of no skill up and a .4 chance of one skill up. You could feed all at once for the guarantee, or you could feed one by one for the gamble. In the end it wouldn't matter and would guarantee players not feel completely cheated.

Since these odds might be a bit high for pad and no one feeds on 1x anyway, it would be plausible to lower it to .5 skill ups chosen per slot meaning a 50% chance of one slot being a skill up slot, or really any other rate for that matter. That would put 2x at one guaranteed every feed, and 3x at 1 or 2 (50/50) per feed, which would at the very least be a much more stable rate.