Well, the fire is calling the kettle black. The manual say not to mount the transceiver vertically! I wonder why?
I own a 480 do you??? I have also had mine apart to study its design and add accessories to it have you? I suspect recommendation is because someone would mount it vertically face up, which you do not do for reasons I mentioned and you must of missed. So, rather than try to confuse users, like you, between which way a vertical mount is okay they do not recommend it at all because mounted vertically face up would reduce cooling.
BTW how are your 3/4 wave 440 verticals doing that you said would work great when they do not?