So, I don't know how you do the tile detection in this game, but if you are using the default event commands, then RPG Maker automatically changes the coordinates of the character to the tile it starts moving to even if they aren't on it yet. This works for jumping too. If you want to consider the player's actual position, you need to use their realX, realY properties, which are accessible through script calls.
Though that's a more advanced topic. I'd advise you to check out the list of script calls for MV/MZ if you want to make these sort of more advanced games. This game has a neat concept!