TFC Rick therein is one big challenge...how big of a cut to allow how much hammock/suspension to pass through. As you saw in the vid the Ponderosa luckily has that second zipper so it can 'expand-contract' to suit.....so maybe add a zipper? and if so it wouldn't have to be a foot long like on the Ponderosa.
'fleece or anything in the foot pocket' I'm not following you on this...did we add anything to block air you mean? No, the zipper shuts down really close to the suspension leaving.
Now when Poof uses it she needs to push any unused clothing down that way just to fill in any air pockets so as not to have to heat.