As long as you can get aligned behind the sight, it should work without issue, but usually offset mounts tend to place the optic fairly close to the weapon, potentially making the space even more cramped. Moreover, using a riser under an offset mount may not really help things, depending on the mount combination, as it may not significantly change the optic's location on the vertical plane once the rifle is rotated.

This is not to say that offset sights are not viable if you can figure out a way to make them work, but it will be fairly dependent on the specific configurations/individuals, more so, IMHO, than optics mounted on the top rail, as there is so much variation in the different mounts/configurations with no real "standard."

For passive aiming, 12 o'clock mounting is probably the easiest solution, or, even mounted in an offset ring to the optic, rather than the receiver, but this will depend in part, at least, on what you're mounting the RMR for. If you're mounting it as an alternative to BUIS, then that may be a concern (though hypothetically speaking at least, a scope could break in such a way that did not disable the RMR, e.g., fogging inside the scope). A lot of folks, particularly those doing a lot of night work have eventually ended up foregoing BUIS entirely (not very useful at night anyways, can get in the way of other accessories, etc.), but if you want to keep BUIS as many do, it's best to consider BUIS one thing, and supplementary sighting systems to be another thing.

~Augee