I had a bit of time to fiddle with this yesterday and came up with the numbers needed to mimic the behaviour of dragging volume automation from above the line (i.e. so that each node retains the same distance in db from the next one - more or less).
To work this out, I put a node at every point on two adjacent, zoomed tracks. I then dragged the first track up by the increment I wanted to measure (always referencing a node that would end up at either +5.9 or +6.0db) and next adjusted the second track with the transform window, until each node on each track was at an identical level. (It was actually a lot quicker to do than it sounds!).
The results are as follows:
For accurate global volume changes, in step 9 of my first post, choose "Mul" at data byte 2 and, for the following volume increases, enter the following values:
12db = 2.000
10.5db = 1.8284
9db = 1.6840
7.5db = 1.5388
6db = 1.4138
4.5db = 1.2969
3db = 1.1914
1.5db = 1.0977
1db = 1.0585
0.5db = 1.0352
0.2db = 1.0195
I have saved these as Transform Sets, so it is now very quick for me to perform volume increases across multiple tracks. That said, I still think that using the Gain plug-in, the master fader, or sending tracks to a buss for global volume changes are all effective (and in some cases a better) options - but this has its place too.
These numbers can also be used to decrease the volume by selecting "Div" at data byte 2. However, unlike with volume increases, the results are not 100% accurate. If I get around to working out what the exact numbers should be for volume decreases, I will post them, but if anyone else wishes to do it, please feel free!
N.B. It is important to perform any volume increase in as few steps as possible. If you want a 6db increase, do it in one 6db step and not six 1db steps, as nodes at lower levels will not be changed at all if you use 1db steps. This is true, also, when dragging automation.