Hi, I've been working on learning to speed run this game and have been struggling to understand the correct positioning to damage boost onto the boss's hands for Rusty Ruins 3 to get the quick kill on the boss, being able to perform it purely by chance usually. Any advice on correct positioning to performing this trick would be appreciated.

Well, the best way is to watch pb's from this game. In my video you can see it exactly on minute 6:37. You have to get Sonic aligned diagonally, rather than parallel to the squares, right before the jump. Once on the boss's hands just press forward and jump. Look at the shadow movement during the hits, that's the direction you must take before the damage boost.