I found this by accident when I created my tas and didn't realize this until weeks later, weird. The only reason I didn't notice it was bc I played my tas in slo-mo if u get any sort of air time, as long as you don't lose high speed, your boost meter increases like 4-5x I'm currently testing all tracks bc this might save a few min of the tas however, there are flaws, air time decreases your speed and you can't lose it at all otherwise the boost meter bonus resets

edit, after further testing, this is built into the game if u keep high speed and drift while maintaining high speed, you get a 2x combo 3x if you fall from a height. this would change up how i see driving in this game.

TLDR: drifting + high speed = 2x boost; changes the entire playing field for his game

Ill call this mechanic "Combo Boosting"