There is nothing about the general M1 spec that resolves the issue with Corsair's power plug being right up against the edge, and the direction of the M1's internal power extension. An ATX power supply has to be mounted width-wise, so there's no option to flip it around and let the cable go off into the interior of the case; the problem the other user had with the 850 seems like it applies equally to your 860 (from what I can see of it).
The other alternatives discussed for resolving the problem include trying to source an angled low-profile power extension/plug going in one of the 3 other possible directions from the default to mod the one that came with the M1, or to crack open the PSU and flip the connector over.
I neglected to mention the power cord orientation... doh! Good catch!