Hi there, Sarah
Well I had to go back to your initial introduction post to see how old your kittens were! So at 6 months, feeding them about 3 or 4 scheduled meals sounds about right. You say you're feeding him wet, but how much wet food is in per meal? One 3 oz can is about 85 grams, so perhaps if you feed him 1/2 of that or 3/4 of that can to see how much he'll eat in a sitting? I don't know about you, but I started feeding my two on mainly wet food diet when they were as young as 4-5 months old, as I found out it's healthier for them, especially male cats. Kittens require a lot more food because they burn up most of their energy by playing but also growing! Since he already likes wet food, I'd try to offer small portions of wet food throughout the day, and make the last meal of the night right before you go to bed but make it the biggest meal for him. And I wouldn't leave a FULL bowl of dry out at all. Instead, I'd leave a portioned amount, a measured 1/4 cup out overnight only. The thing with free-feeding is, you don't know who is eating what or how much. If one cat eats more than the other, and the other is lacking appetite or skips meals altogether, you probably wouldn't notice his sickness until maybe too late. So, giving scheduled meals makes more sense to know the health of your cat, and catch inappetence early on.
Also, investing in a great interactive toy, like the "flying frenzy" cat toy in the UK for at least 20-30 minutes in the afternoon and before his last meal can help tire him out. You just need to make sure that Rocky is so~~~~ exhausted that he needs to lay on his side and literally panting before you call it quits. Kittens will have boundless energy, so making this routine a few times a day will most likely help get him to tire out more quickly and rest throughout the night. Don't forget to feed his last BIG wet meal after this. This will put him in grooming mode after, and then help him doze off, hopefully throughout the night.
Consistency with all this can only help you get more sleep! Good luck!