Anti-Aliasing of touching panels

Hoping I have missed something obvious. I want to use Anti Aliasing for a stylebox applied to a panel, but I also want these panels to be seamless (they are in a VBoxContainer).

With Anti-Aliasing off, this works where the top and bottom panel are indistinguishable, but then the exterior corners suffer.

Turn anti-aliasing on, suddenly there’s a seam.

Ideally you’d be able to dictate which edges AA applies to, but is there some other way to achieve this I’m not seeing?

Using a separation constant of -1 helps, but isn’t perfect:
image