I think the components on the Enviro+ board contribute some heat. The gas sensor has heaters in it and is fed via resistors. So I think that is why active cooling works better than a long cable. A better solution might be to separate the BME sensor and put it on a long lead.
I have never seen any official response about Enviro+. The gas sensors seem next to useless because they seem to respond to humidity, temperature and pressure more than gas. They also seem to take days to stabilise after being turned on.
I haven’t shared the case design because I regard it as a bit of a fail. The fan I used is too loud.