Hi hun, I would say 2 x feeding is about right then. Many continue this until solids are firmly established until 7-8mo when ebf.
It looks like you've got a good routine going, however it would look at starting to extend the A times around now. As he was born a month early and we look at his adjusted age, we'd still be looking at closer to 2hrs A time rather than 1.5.
I would look at extending it gradually, so maybe extend by 15mins, hold it for a few days and see what happens. If the short naps return or stay, I'd extend again by the same amount.
How often are the feeds spaced? And how much is he taking during the day if I may ask? Ebf bubbas tend to only manage a max of 3hrs between feeds, I wonder if the day sleep is taking away from an extra feed being in there somewhere? There's also a huge GS at around 4-4.5mo that needs an extra feed in there too. Is he draining all his bottles? If so, we recommend adding an extra oz or two so he leaves a little, at least then you know he's stopping because he's full and not because the milk has come to an end iykwim? Xx