You're getting a little closer to it, though after reading both of your posts we may not be on the same page. The really sticky part has to do with when files (front and rear rank) dress (left or right)...it should only be when an entire file (front and rear) adjacent to them has been eliminated from the line. What you mentioned in your first post (front rank dresses over, then half the rear rank steps up to fill gaps), would really throw the line into a mess since you would have tall, short, tall from right to left in the front rank, and as more casualties mount it would get even worse. Also, the command structure would begin to break down since the different squads and platoons would begin to become intermixed. This is not much of a problem in reenacting since squads and platoons are rarely used, but at the time of the war it would be much more important.

Shifting down gradually only as files are eliminated as I mentioned before will keep the order of the line preserved, and keep the frontage occupied at a greater width for a longer time. The heights of the men do not cause the same sorts of problems in the way I have mentioned since the differences in men near each other is all relative. For this I'll have to explain the correct sizing of the line (which is done incorrectly by many reenacting units). Here are some basics for sizing the line, I'll keep it a bit simple for now, and for these examples we will only deal with privates, no corporals, sergeants, officers, or file closers. These principles come from Gilham's Manual, and are about the same in Hardee, Casey, and even go back as far as Von Steuben and earlier.

Let's say we have a small unit of men to size (we'll keep it small at 10 men). The men will line up in a single rank. The rank than faces to the right, and if any man is taller than the man in his front, he will switch places with that man and so on. Once this has been done for all the men you will have a line faced to the right that is tallest to shortest. After the rest of the process is finished, the right flank of the company will be taller than the left, (keep in mind that this can also be done in reverse so that when the process is finished you will have the right flank of a company being shortest instead). So for the line below facing to the right, 2 is shorter than 1, 7 is shorted than 4 and so on.

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After this single line is adjusted there are several commands that could be given...in this case we want to have the line face to the front. Then have the rank "Count 2's", this makes every man a 1 or a 2 (even or odd in the diagram). Next the command is given to "Right Face", at this the rank will face to the right, the even files (2's) will step up on the LEFT side of the odd files (1's), then the command will be given to "Front"...the resulting ranks appear thus:

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This is where it is easier to see that the height of the men is relative to the men near them...i.e. 2 is shorter than 1, but he is taller than 3 & 4 (and everyone else).

Now let's look at how the line adjusts if certain men are hit.
Let's say 8 gets hit/killed...7 steps up

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If 6 is hit, 5 steps up

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Notice that there are adjacent gaps in the rear rank, but they have not dressed to the right yet. For that to happen, not 7 or 5 or both would need to be hit...let's say 7 gets hit.

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Basically this keeps the unit compressing at a controllable rate, keeps squad and platoon integrity maintained and still keeps height order within the line.

I think this covers most of what you asked in your last 2 posts. Just remember not every reenactment unit does everything correctly, and not every company is tall to short from right to left...usually it should alternate to maintain and average height appearance within the battalion (1st Co. tall to short, 2nd. Co. short to tall, 3rd Co. tall to short, and so on). By butting tall ends against each other and shorts, the appearance of an average (and visually taller/more intimidating) unit is presented to the enemy.

Josh