Don’t take this as gospel as I am not very good, but I recon most of the commercial carp groundbaits would be ideal as they are rich in attractors and are fairly sticky. I would definitely bulk the mix out at least 50/50 with brown crumb though and I would definitely pass the dry mix through a medium sieve to make sure its nice and fine, don’t throw the bigger particles away, blend them in your wife’s food processor and pass them back through the sieve. Premix it to make it inactive, then pass it through a riddle. I know for certain skimmers and bream eat this mix because I have used it before in a feeder and caught well.
That should give you a good base mix to work with.

One thing I would definitely add though, would be casters, as skimmers love grazing for these. I would also add a little bit of sweetcorn as this will attract and hold the bigger fish.
You could even add a small sprinkling of soaked micros, if you intend to fish an expander over the top.

I’m not sure about hook in the loop in deep water, but you want something positive to get the bait quickly and then show up the bites.

My mix for a similar venue I fish is 50% Sensas Green IM5 (which is very fine and virtually all passes through flour sieve) and 50% sensas lake (tend to sieve at this time of year as well).

The IM5 is a good tacky groundbait (it can on its own be used as a paste in warmer times!). As a result get the mix right and the balls will stay firm. I would endorse mixing the night before. Finished product is a good darkish colour.

Adding casters and a finely chopped lob worm a must plus a couple of grains of corn.

Not sure of the benefits of HITL for that depth other than you have a couple of big shot near your hook. Would probably look at double bulking.

Double bulking IMO

HITL will work fine at that depth. As for groundbait I would use DB green swimstem with DB method mix to make it stickier. Or I would substitute the method mix for 2mm course pellets, caster and fish tank gravel to plummet it down

I’d go with 1/3 Secret, 1/3 Lake & 1/3 green swim stim.

1/3 Black super bremes. 1/3 lake. 1/3 leam.

green swimstim and dynamite canal/lake.

HITL will work fine if there is not to much tow. If Pellets are used on the water it mabe worth trying a swim just fishing and feeding them.

Could be worth adding Sensas Collix or PV1 Collant to bind the mix and add weight to the mix. Collix has zero feed value but binds the mix and adds weight to make it sink like a stone and comes in a shaker and is easy to add to mixes. PV1 collant is a heavier binder which also adds a sweetness to the mix.