Two pieces of feedback about the downward boost.
First, I use a keyboard to play the game (hooking up a mouse is kinda inconvenient), so it took me a while to figure out how to make the down-boost work. The game says you need to hit 'f,' but you seemingly need to hit 'F'—like, shift+'f'. That's inconvenient and weird.
Second, it took me a while to confirm that that's (part of) what's going on, because the circumstances when I can down-boost are unclear. It seems you need to be at just the right altitude (for some reason), but sometimes it seems like the you-can-boost arrow flickers into and out of existence...maybe as the targets it's pointing at move away and new ones come into being? I have no idea how it's supposed to work, so maybe my description is way off, but the fact that I have no idea how it's supposed to work is kinda the problem?