You could put a larger sensor on the carrier, that's one option. You could also attach a dedicated sensor platform to the fleet..basically some engines and fuel built around a massive sensor. That needs protection tho, as it's basically a homing beacon for the enemy. You probably won't be able to match sensor range to fighter range and you don't have to. You have to consider return trips and loiter time as well. But your current ratio is somewhat off. As a completely different option, you could scratch some fuel from the fighters, that gives you either smaller fighters which you can carry more of, or you use the saved space for another gun, leaving it at the same size.
And as for the ship sizes: I'm just giving my opinion, it's by no means taken to be definitive. I'm just a big fan of a smaller fleet of heavier ships, instead of having the same tonnage in a lot more individual ships. Aside from the initial setup (shipyards and facilities) I find the larger ships take a load off the support structure. If I have a strikegroup of 7 ships that is battle worthy for what I need, I need a jump tender that can take 8 ships (indlucing itself) on a squadron transit in one go. If I have smaller ships but need, say, 13 of them to be battle worthy, I'm gonna need a jump tender able to ferry 14 ships (which is vastly expensive tech) or I need multiple tenders and split up the fleet, or I need to use one tender and move it back and forth, which leads to delayed arrival. Also, a bigger missile ship can take more ordnance, potentially even enough to last an entire engagement without needing a collier close at hand..and still have a usefully large salvo size.