If looks like the bottom of your character collider is still over the floor collider, hence it’s not triggering the fall.
Decrease the radius of your CapsuleComponent (under section Shape > Capsule Radius). The downside of this is it will allow your character to get closer to walls and other obstacles.
Edit: Sorry, I just re-read you post. You could try and dynamically assign the Capsule Radius based on the scale of the character. Alternatively, you can try and use line tracing from your legs down and temporarily disable capsule collision when nothing is detected, but this might be expensive on the performance if done per frame.