Any reason why the different max level variants level up at different speeds? Mistake or intended because isn't that what the standard and fast variants are for? I first tried to use the max lvl 20 standard version and ended up with lvl 16 in my save game. Then I tried the max lvl 25 standard version and instead ended up at lvl 18
Yes, there is. Without a way to completely decouple story point gain from leveling up, the only way to make story point gain... 'balanced' in comparison to vanilla, while also staying close-ish to vanilla style-levelling, is to smoothly transition from low experience required to high experience required. And the different level caps means that you end up with different rates. I tried to keep them as close together as possible, and switching between the two won't cause any problems. Let's say you're using the max 25 and switch down to max 20, you'll still be at the higher level, you'll just have an experience defecit to makeup until you can start levelling up again.
When I first made this, I really made it for myself and only myself, but figured that if I went through the effort of coming up with a 'balanced' max-level increasing mod, I might as well upload it. And then I figured "well, I already have a good system for figuring out what a 'balanced' leveling rate is, why don't I apply it to other increments of 5 and upload those?"