I’d like to know that, too. IMHO, it can’t be done, since it would imply the double of darkness into one single slot.

One solution I have found is to reduce the weight of the stroke in the composite characters, so visually it has the same darkness as 'normal' characters.

This is Capibara Mono by Caketype

Yes, that could be a solution. Seems to work in text sizes (not so sure, though). But in bigger sizes it just looks too light.

Nick, are you suggesting there is no problem?

It's the same problem as "m" if the face is reduced to a perpendicular grid.
In another execution, such as a serifed, contrasted-stroke italic, it would be a different problem, and more of a problem:

I understand.

It might just be my own design, that has an open feeling (and where the M doesn't have three verticals), in which the combined characters seem to feel out of place.