The bullet is actually not pure reflect, the direction is Bullet position relative to player, for example if bullet is 45 degree to the right, it would hit 45 degree right back, (not true reflection with normal vector like light bouncing off a plane, did that and it’s uncontrollable Lol). I tried a few time and it’s very consistent to reflect a certain direction, if you want to hit left ward just put your self to the right relatively. It’s better than Auto-aiming as you can aim a certain direction rather than the game deciding too, and larger bullets later on have incentive to aim in different direction like towards the wall or specific big targets.

Some bullets is very sparse to hit and that’s actually very deliberate, it’s mostly to emphasize the fact that you should hit the large cluster bullet or larger bullet (splitting, lasers spawning, etc) instead. The jam time ran out early so didn’t had as much time to design stages, but it is 80% deliberate that some section have very little “hittable”. For example Section 2 the green spike spam is too spaced out to hit properly, but occasionally a red fairy spawn cluster red ball that can clean entire board if hit fully charged (as charge also increase range, making it possible to hit entire thing)

Edit: Section Before Junko is a few exception though, there is no real deliberate cluster so you’ll have to figure it itself, 

- 3-1 you can hit when red circle groups inward; 

- 3-2 you hit the circle intersection fully charged, you save the hit only when the the star fairy comes in, then do little hit to clear gaps

- 3-3 is aiming heavy, you hit the rain/ice bullet to kill the fairy before it spawn the red circle which gets out of hand fast. This section is just a Stage 6 LOLK reference lol

- Junko herself you hit to the side of her, the laser deals majority damage and can hit her without her able to hit back. If it’s too fast paced you can slow hit a ball sidewards on your side and it remains stuck