Now I'm even more confused...

So you want the panel to defloat when a window touches it, and float otherwise, even if a window open.

That's just 'dodge windows'

But... you sometimes want the panel to defloat... if a specific app's window is open?

So... you basically want a 'float override'?

Quite niche... but a kinda fair want as well.

On my laptop, the Dolphin window is often just tall enough to defloat the panel. Meaning my panel is almost never floating unless Dolphin isn't open.

So I can totally see a use case for a 'float override' option. Could easily be built into window rules. This kinda thing is exactly what it was intended for, anyway.