Well i try to share all the thoughts i have when i try a game and i know i can sometimes end up in a bit of a wall of text territory ^^'
No problem, from what i experienced since i started my gamedev journey with Godot is that raycasts can sometimes act strangely, i know i've even had my issues with them for this jam so i understand, and like you said your game works fine without the bounding line trajectory, although hvaing bouncing surfaces for the particles could ba a cool way to expand if you plan on adding to it post jam :)
If i get some time after the jam is done i'll see when i can check it out, and i do understand not having much gamefeel for a jam entry cause this really can take some time to add and i know i've had several times where my games lacked any kind of proper feedback at least on intial relase during jams ^^