We already do gfmoto. As you said with the CF Moto Z8 factory Roof, the air comes up under the roof and circulates downward, plus hot air rises. With the design of the CF Moto factory roof we prefer to go low with the vents for added circulation and let the hot air escape at the top. If you are going to use a Pacific Eagle Roof, then the Vents would be near the top. So it all depends on your configuration. On Jason's RZR 1000, we added our Dual Vents near the top. We didn't know a lot about the type of roof Jason had, so for that very reason, we went high. When ordering you can specify where you would like the vents, but just make sure there won't be a problem with crossbars on your UTV model.
You're right about front & rear vents in Lexan Panels, they give you more control over the comfort levels in your Cab.
The photos are our Lexan Back Panels on Jason's RZR 1000 showing the Dual Vents up high.