I'm looking ahead to getting a better red dot sight if the factory-installed MP-100 on my new M&P 15-22 doesn't pan out. I'm seriously considering the Sig Romeo5, but there are options for riser heights and I'm not sure which height would be best for this rifle. The least expensive Romeo5 has a fixed 1.41" riser. Would that work OK with the 15-22? Is it even worth trying a low profile riser (the second least expensive Romeo5)?

Based on what I've gleaned from Google searches, the 1.41" height appears to be the best one offered by Sig when it comes to the M&P 15-22.

Sportsman's Outdoor Superstore currently has the Sig Romeo 5, model number SOR50000 (1.41" riser only, i.e. no low-profile riser), for $100 as part of their Cyber Week deals. I just ordered one.

Sig Sauer Romeo 5 1x20 MM Red Dot Sight 2 MOA Black Finish | Sportsman's Outdoor Superstore

For the record, I have no affiliation with Sportsman's Outdoor.

I'm considering buying one to, the price is very affordable and I like that it shuts off automatically after a couple of hours, least that's what I've heard.
So far the reviews I've listened to have been pretty positive, those who complain are not happy that it's not more expensive.

I have one on the home defense carbine. Works fine. Auto-on is very sensitive; too sensitive for riding in a car, but works in a closet. The riser height coordinates with the M4 front sight. Shuts off in a few minutes of stillness. And comes on at the slightest movement. Size of red dot is adjustable. I recommend it.

Is this a reasonable setup for the optic and backup Magpul sights? Should the rear Magpul be on the muzzle side of the optic or on the breech side? I can still see the front sight through the optic, but I’m not sure how distorted it is from an aiming standpoint.

This is the right way to do it. If you set the rear iron sight too far forward, you won't be able to see through it to acquire the front sight easily.

Since the red dot is not sensitive to eye relief, set it wherever works for you.