Can't detect collision with nested Area2D

Godot Version

4.3

Question

I have an RTS unit selection system that currently selects all units it collides with. The unit collision box is the right size for colliding with other units, but it’s too large for selections to be accurate. I tried setting up a second smaller collision box, but I can’t detect it with the box select.

image

I am trying to detect BoxSelectCollision.

This is my box select scene:

image

I have BoxSelectCollision on layer 3, with Monitoring and Monitorable both enabled:

The box select has mask 3, with Monitoring and Monitorable both enabled:

I can always detect the root CharacterBody2D when I match the box select mask to the CharacterBody’s layer, but BoxSelectCollision is never collided with.

What’s going on here? I’ve seen some other forum posts about similar issues, but they always end with “You’re wrong, this works fine” without further explanation or the original poster moving to another project.

To detect an Area2D from another Area2D you’d need area_entered signal