Blaze, you mention the end openings of the PolarPod being a source of considerable heat loss, and they certainly could be. But when using my PeaPod, especially with my shorter hammocks- those 10 ft or under but even shorter is better for this- I tightly cinch the ends down near the hammock end knot. This seems to keep the warmth in pretty good, though there is always at least a tiny hole for some leaking.
Do you do this with the PolarPod? Another thing have occasionally done is stuff something up into that area of the hammock, completely blocking even the tiny vent. Of course, you have to have something available for that job.
Often, when my face vent is really small, my head and face are the warmest part of my body using the PeaPod. I often have to remove my hood or hat.
For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us....that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God. For we know that the whole creation groans and suffers the pains of childbirth together until now.