I am looking for an estimated total, maximum depth of wet grain plus 1?-2? of water above the bed.

When a calculation doesn't help, I'll default to a pretty good rule of thumb.

Generally, the maximum water & grain a mashtun can hold is equal to 70% of the total volume in quarts (above the false bottom).

If you calculate the cylinder volume and divide by 231 the again by the height, you have the gallons contained in each inch.

If your mashtun were 28" wide and a total of 36" high, it would hold about 96 gallons. Using my above RoT, you could cram about 269 lbs in with water.

Your solution is probably to convert the water additions into weight and a corresponding weight per inch of the mashtun.

Let's say that you're using 140 lbs of grain to make a batch. The maximum grain weight (269#) divided by the height (36") is 7.47 lbs/inch. Nevermind that you'll use a false bottom or that you might have deadspace. We only care about the weight per inch, at this point.

If you're a traditional mash thickness guy, then you're using 1.33 quarts water per lb, which is 9.92 quarts per inch. Convert to weight and you have 20.7 lbs per inch. Add the two together and you get 28.17 lbs/inch.

This means that a 140# grist with traditional liquor should stand about 19" above the false bottom. If you're aiming for your coil to float somewhere around halfway, the coil center should be at about 9.5" off the false bottom.

There will be a minor amount of displacement from air, but it will not change the overall depth by much.

As with most pro brewing, staying away from volume measurements and using weight for all liquids leads to more accuracy, no matter what temperature. It also leads to less waste and more profit.