B4 in the modal voice is an incredibly difficult note to reach! Who are you listening to that goes higher than that? The big note in Nessun Dorma is a B4 for Christ's sake! I consider myself very lucky to have the vocal range I have, I've got a decent tenor range that covers me for everything I want to sing. And despite that, there's no way I'm hitting a C5 in my modal voice, not even CLOSE!
Perhaps what you really need to work on is improving the quality of your falsetto register: if you don't use it all that much when you sing then it's probably quite weak: you don't use that part of your voice often when you speak, so it rarely gets used at all. You need to practice singing in your falsetto so that you feel fully in control of both of your vocal registers. You also want to train the low end of your falsetto, so that you have as much overlap between your 2 vocal registers as possible.
You need to give yourself the physical tools to make the best performance choices about how you sing a passage that you know will at some point end up in your falsetto range: choose the point at which you transition based on what makes sense musically, rather than just going up and up until you run out of modal voice and then "making do with falsetto". And, similarly, if you know a certain passage will bring you into your falsetto range, you need to consider how much "power" you're going to give the modal voice notes leading up to it, in order that the falsetto notes don't seem underwhelming.
This answer applies less to classically trained opera singers, who I believe rarely use falsetto, and also have a very different singing technique that functionally maximises the range physically possible from a singer.
