Perhaps I had better explain a bit more what my hood looks like and how I use it in the cold. I am not sure the word 'hood' means the same thing to everyone.
Imaging a quilt with the bottom sewn together for a foot box, or a single tapered hoodless bag with a 3/4 length zip. Now add a generous semi-circular extension to the top end in the middle. This is my hood. It can be opened out flat: there are no fancies in the design. I made these two bags (wife and me) myself - quite easy to do.
In the cold, I snuggle down into the bag (which is long enough!) and throw the hood right over the top of my head. The edge of the hood does actually touch the ground or my mat all the way around. I usually pull it back from face a bit if I am warm enough. In addition, the sides flop down on either side of my air mat: the quilt is not so narrrow that I am struggling to get a ground seal. If it's real cold, the breathing gap may collapse for a while, but this doesn't worry me. Enough oxygen diffuses in for me. My wife likes to wear a fleece cap/hood as well, but she doesn't like the hood over her head so much.
But this means that there are no gaps around my body and head for drafts. So if the lay of the quilt over my body is a bit loose, this doesn't matter. The air inside warms up real quick - especially if am breathing out under the bag. So-called 'dead' air does not matter!
This does require that the bag be not absolutely minimal in dimensions. True. It would be a little lighter if I made it shorter and narrower. But the savings would not be that great, while the potential for drafts and loss of warmth would be high. But the benefits of the generous size are enormous flexibility and comfort. I can sleep in any position I choose.
In hot weather I can simply push the bag downwards, off my head and shoulders, and let some drafts in. If it is a really hot Australian summer night, I may actually sleep on top of my mat without the bag above my knees - this has happened!
Sure, it would be nice to have lots of bags with a fine gradation of performance, but most of us lack the dollars and the storage space. (Don't forget the latter!) So a bag which can go from 30 F to 100 F isn't bad value.
As it is, this bag has taken me down to freezing with me wearing thermals, and to -5 C (23 F) with a very light quilt over the top. But I do sleep next to my wife! You should never underestimate the value of having a warm sleeping partner. But I hesitate to include this under 'unconventional sleep systems'!
250 g Pertex microlight shell 8.8 oz
300 g of 800 loft down 10.6 oz
That's 550 g total 19.4 oz
Spare quilt 150 g of down 5.3 oz (shell not included - cheap and heavy)
My (our) current thinking is to keep these bags for winter snow trips by adding a UL quilt with about 300 g of 800 loft down to go over the two of us. A bit of a single-layer foot box at the bottom to go under our feet, and maybe something at the top corners to control the top end. Maybe a bit of string to tie to some other gear - movable rather than fixed under the mat?