I was having the same problem so I stated using a modified 3-2-1 method. Starting with 2.5 hours, then foil wrapped for 1.5 hours (with honey and Turbinado sugar) and then up to an hour sauced and unwrapped until tender. They are not fall-off-the-bone but have a little resistance which is what we like. I agree bottom ribs near the coals get darker but are usually OK. I use a second hook to keep the rack raised higher above the coals to minimize the charring during the first 2.5 hours This is not practical if you are doing 6 racks
I might have to try wrapping next time. I don't want fall off the bone but I do want a nice pull with clean bones afterwards. I've avoided the 3-2-1 for the simple fact that i like the nice bark which tends to soften when wrapped. Do you rehang them after wrapping of put them on the grate?
I again hang them when foiled. If you do this, make sure the bottom is good and sealed otherwise the liquid will run over the coals. As the ribs are on the coals after the foiling for the last part, the bark is still there and caramelizes nice with the sauce. No two racks are the same so watch them until they are tender enough for your liking.