Marine Kelley has posted that a new version of the RLViewer is out.
This version has the new Hover Height adjustment. Right-click your avatar and adjust away. The adjustment is saved as a setting and so, persists across logins.
Marine points out that ONLY viewers with this new feature can see the results of your adjustment. I expect most viewers will have this feature with their next release.
This Height feature is not yet integrated with RLV commends. So, the RLV scripting comment @adjustheight may produce unpredictable results. Marine is promising to get this fixed, may be by the next update.
There was a bug in RLV that caused problems with attachments when logging on. That is fixed now.
A new 10 clothing items per layer feature was added some time ago, in the preceding release this feature was lost. It has been added back and this viewer allows 10 clothing items per layer. Expect this to change in the near future. The Lab has changed limits for clothing layers. They are going to a max of 60 layer-able clothing items for the avatar with as many on any one layer as you want up to the limit. The change should solve some problems that are making for some tedious work-around routines when dressing.
The full story of the Z-Offset (Height Adjustment) is here.