I'd like to chamfer the interior corner circled in red on this part:

I can do a corner chamfer on the exterior corner (circled in blue), but attempting the same on the red-circled corner errors with the message "Could not build chamfer due to geometry conditions..." The lengths of all the adjacent edges are ~7mm, so it's not a case of the chamfer being too large. It seems that only exterior corners are valid targets for corner chamfers?

I'd like the triangular face to be angled so I can possibly print this part without needing supports (we're looking at the bottom). The height of the orange edge does have to be controlled.

Any suggestions for achieving this? My first thought would be to hog out the cavity with a combine-subtract (and as noted, I can apply the desired chamfers to the tool body) instead of the rectangular cut-extrude I've used here, but there's a whole bunch of similar cavities and I was hoping to find a solution without having to make multiple instances of anything.

The part in question, for those motivated:

Thanks for the help!

-Dan B.