Copper flashing = heat strap = no-cut ESC cooling solution?

On one of my boards I conduct some of the heat away to an external heatsink, through the ESC mounting bolts (not copper) that go through the enclosure. It does seem to work okay-ish if you’re not pulling huge currents. The external heatsink does get hot. It’s a much more muted phenomenon than a directly mounted heatsink though.

You can’t see but there is a thin air gap between the aluminum plate and the enclosure wall.