I'm sure it will sound ok, but the drivers are designed to have a horizontal dispersion when in a horizontal orientation, if you flip the speaker in no longer has the same qualities. Would be no different than laying a regular M80 on its side, you wouldn't normally do this.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85