The way I've heard it, each addition of 4096 to the Thing type adds an extra z-offset equivalent to the maximum height value of that Thing. For example, if the maximum height of the Thing is 2048 fracunits, its z-offset is 512, and 4096 is added to the Thing type, that should set the height at 2560.
If you ask me, I think it's time to create an entirely new SRB2DB, built off the code for Doom Builder 2. This would be an arduous venture, but it would be well worth it, as DB2 has some awesome features unheard of in our editor, such as displaying sector floor flats in the standard editing modes. If we could only throw in support for SRB2DB-exclusive features and, yes, the ability to recognize bitset stacking, we would have the ultimate SRB2 level creator.