MM6 Avoiding whiffed shots against Mechazaurus

Against Mechazaurus you'll notice that sometimes when you hit him with a Yamato Spear nothing happens - the shot doesn't do damage, but it also doesn't tink off like normal. This happens when you hit the boss' vulnerable and invulnerable hitboxes on the same frame. On Mechazaurus they overlap in such a way that the area with vulnerable hitbox only is only four pixels wide. Yamato Spear travels six pixels a frame, so it's possible to shoot it in a way that skips over that area and ends up immediately on the invulnerable hitbox.

Whether your shot hits properly is completely up to the horizontal position you're shooting it from. You can imagine the room being divided into stripes where you have alternating four pixels where your shot will hit normally and two pixels where it will get eaten. You can either shoot from a known good position - back against the left wall works, or you could figure out a visual clue for one of the four-pixel areas elsewhere in the room - or you can doubletap while holding right which makes it unlikely for both shots to come from the bad two-pixel areas.