Thank you very much! The difficulty ramp is between the 3rd and the 4th; I planned a level between those two to make the shift less dramatic but I couldn't make it because of the tight timeframe.
Of course I'm willing to divulge, I love talking about these things! I think I used the least elegant solution possible, but basically I gave four 1024-pixels-long raycasts to the player, with directions right, up, left and down. Then to the moving objects (enemies), keys and doors, I gave an additional Area2D with an expanded CollisionShape2D, so the raycasts can collide with these additional areas (in the enemies' case, the areas cover their path), while the player collides only with the physical object. I could go in more detail, but I think a private messaging system would be better (also I would need time to recollect ideas and explain in a decent way the details :'D)
As for the tweak you're suggesting, I don't know why I didn't thought of it before. Thanks for telling me, if you're okay with it, I will update the game with it in the future after the Jam is completely over!