You have the M5s so you're familiar with their excellent off-axis characteristics. The tweeter is quite linear to about 60 degrees and the mid to about 45 degrees. Beyond that, they don't sound bad but their character does change.

If you place them with their mids 4 feet ahead of your MLP, assuming your ears are about 3 feet off the floor, you'll be within the range of the above angles.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated