lets assume its a small humanoid, 2 legs 2 arms etc. riding a small size cat using a starknife. am i able to attack into adj squares with my tiny humanoid without a reach weapon? if not is there any way to do it without changing my size or weapon.
If you want to be able to attack your opponents without reach, Escape route feat, shared with your mount, will help you to avoid AoOs while moving into the opponent's square.
Either play Hunter, or get the Horsemaster's saddle.