David,
"cut some "fingers" around the neck"
Like in the photos below? It does address the bulbous head problem and was comfortable to wear. I also like the jester look it gives me.


"the foam pad splays out during the night"
I sleep upon the pad without splaying it so I get a double pad under me in this area. So 1/4" foam vest gives 1/2" under me; 3/8" foam vest gives 3/4" under me, etc.
The pad in the attached "jester" photos just rolls out like a normal pad. But notice the boxy shoulders. They make it hard pull a windbreaker over them. With thinner, flexible foam vests (e.g. 1/8" thick) it isn't much of a problem but it is with the thicker/stiffer stuff. The sloped shoulders on the vest in my original post address this problem. The splayed out shape of the vest is a by product of the sloped shoulders.
"what if you don't cut the sternum-to-belly-button cut in the foam?"
I've tried it with and without the sternum surgery. Both work. The sliced sternum model is easier to get on and off and the flexibility of the separate front pieces makes it feel more comfortable when wearing it. The front opening is also nice for venting if I get too warm. The sloped shoulder model cannot be splayed without the sternum slice and with the sternum slice it splays out in that Y like shape.
"I'd imagine that the outer windbreaker is a huge factor in retaining or shedding heat. Worn just as a vest, it would add some warmth, but only with the windbreaker does the assembly become a jacket."
I agree. The open design of the slit sternum model, in particular, results in almost no warmth if worn alone. The warmth just blows away. Neither the fishnet nor the foam vest can retain much warmth without being covered/contained.
The float coats I'm been wearing, however, work wonderfully without anything else. So the 1.5 pound float coat can replace base layer, insulation layer and outer layer (including raincoat). These 3 replaced layers could easily add up to 1.5 pounds. I'd still like to reduce the weight of the float coat or its alternative, however.
"It makes me wonder what the thinnest, lightest velcro-like material is and could you use it to seal up the side so (1) you'd be even warmer and (2) it would have more warmth as a vest."
I agree. I've experimented with various options in this area…..without success. Everything I've tried turns out to be more trouble than its worth, uncomfortable or too restrictive to venting. I'm not a very good tailor. I know there is a better way to do this.
Thanks for the ideas,
Daryl