Both of the "quad mixes" (note usage of ironic quotation marks) that Westbound issued (this one, and Ohio Players 'Ecstacy') are upmixes of some sort of the stereo mix.
The reason the rears sound like they have discrete activity in them occasionally is that on some of the tracks, after they created fake rear speaker action, they rotated the soundstage 90 degrees, so the original stereo mix is in the rear left and front left speakers, and the upmixed junk is in the two right speakers. So as a result of this, your ears prick up occasionally thinking you've heard something behind you, when in fact you're just hearing something from one of the channels of the original stereo mix that's been moved to the back.
It's no wonder these two tapes are as rare as hen's teeth, I'm sure they didn't sell any copies by word of mouth, that's for sure. I saw someone on ebay UK pay over $350 for this tape a year or so ago, and all I can do is feel bad for them.
It's made even more of a shame by the fact that this album (and Parliament/Funkadelic music in general) would be ideal candidates for the surround treatment. When I saw them live about 20 years ago they had more than 20 musicians on stage at the same time, and their 70's studio recordings were no different, an absolute abundance of talent playing together on all of those albums.