Potential Problems With Leaving Feeding Shim On Hive All Winter?

[Alklar20]

I'm planning on getting a shim for feeding bees during the winter either dry sugar via the mountain camp method or sugar cakes (Link: https://hillcobees.com/product/winter-feeding-shim/). It's 1 5/16" tall and has a small notch that serves as an upper entrance for the bees. I was thinking about leaving the shim on the hive all winter because the bees could use the upper entrance in case the bottom entrance got clogged by dead bees during the winter. However, I'm concerned that the empty space the shim would create would cause problems for the hive; for example, heat loss. Are my concerns valid; would there be any problems with leaving the shim on all winter?

Note: The winter setup I have planned for my hive, from the bottom up, is a screened bottom board (not sure whether I'll be closing it up with the mite tray or leaving it open), two deeps, the shim, a moisture quilt, and the outer cover. The moisture quilt I plan on using will be the one at the link I've provided below; it's 3" tall and will be filled with wood shavings.
Link: https://www.funnybugbees.com/hive-components/hive-accessories/inner-hive-covers/Beehive-Ventilation-Shim-10-Frame-quilt-box-p140236073

[Ben Framed]

I used Mountain Camp last year. I am located in Ms zone 7. My shims are about 2 1/2" if I remember correctly. My shims have no gap. It gets pretty cold here at my location at times. 20's at times teens occasionally. Sometimes in the single digits. I am speaking fahrenheit. I have nothing but good things to say about my last year set up.

Remember heat rises, if you have a gap in your shim, heat will escape like smoke from a chimney. As cold air is scuked in the bottom entrance by this vacuum.    Bees have to generate that heat = resources ..

Adding: When mountain camp is used in my area there is no need for a quilt setup as you mentioned. The sugar on top works both as a moisture absorbent and an insulation barrier..

[gww]

My first two years I had 1.5 inch shims full of mountain camp left on all winter.  Had 100 percent survival.  Couple of hints.  They carry a lot out as trash if put on while warm out which I did cause it was easier.  They really hit it early spring when brood rearing starts.  Feeding a couple gal of thick sugar water before first frost might work better and can be done with the shim and gal. zip lock bags 3/4 full two at a time in the same shim.  Make a couple of slits in the up side of the bags with a razor blade.  However shim works good.  I am in Mo.  I did find that leaving them on too long in spring will have the bees building comb in them and so I took them off when I saw the very first bit of wax building or even earlier.  Another hint is to put some chicken wire on the bottom of the shim and as long as you are using blocks of sugar, it is much easier to remove what they have not finished come spring or if you get an early warm spell and want to look at your bees.  I have not fed the last few years and have no upper entrances and would not use a shim just for that purpose but also never get more then 8 or nine inches of snow most times and it does not stick around for long.
Hope this helps.
Cheers
gww

[Ben Framed]

gww I have not used the gallon zip lock bag method. Sounds interesting. Believe it or not, My first winter I used boardman feeders, (I didn't know better), for my freshly split 5 frame nucs and looking back I consider myself lucky, 'very' that I had a mild winter. There was also honey frames in these splits. All 5 survived.. On warmer days they sucked it up from the boardmans. I do not recommend using boardmans, as bees will need to break cluster to feed.. Yes I was very lucky..  All 5 would have probably died had it been last season, considering the end of last seasons' extended deep freeze.

[gww]

I lost some last year that still had honey but not in the top box during that same cold spell.
Cheers
gww