To be honest I generally wrap them in foil and then bury them in the hot ashes. They seem to work out fine
It's not unknown for us to have too many and remove some to lie under the firebowl........and have them for dinner a few days later, and they were very good indeed
I think the best advice is don't be in too much of a hurry. If you want them fast, just boil them.
I do mine in foil and just accept they get burn't, some times smaller spuds and moving them around helps put in more than you think you need and you can normally salvage enough good ones.
you can also use the baked spuds to cook an egg at the same time, cut in half ,hollow out a little from the middle,crack in an egg, put the two halves together again wrap in foil and place in the embers. an easy way to cook eggs if don't have any cooking pots with you.
We used to wrap them in foil and cook them in a coal fire during power cuts and even though the outer layer was burnt black the inside was perfectly edible and especially tasty with a nob of butter. As a young child we seemed to get quite a few extended power cuts in the winter so used to look forward to baked tatties in the fire eaten by tilley lamp and a game of monopoly to pass the evening. This was the only time we ever had baked tatties as a child. And we generally only used smaller tatties as the big ones took too long to cook. As for cooking time take em out every now and then a poke a skewer in to check if it is ready! Just make sure you are not already hungry when you put them on.
Can you imagine my disappointment when microwave ovens appeared and the lack of carbonised tattie skin on my baked tatties!
Don't wrap them in anything. Put them in the ashes at the bottom of a well established fire an leave for about an hour. Sure the outside will burn black & hard, but the core on the inside will taste better than any foil wrapped jacket you've ever had.