I have used these form variables sucessfully in versions of ezPublish prior to the 3.5 series. However there seems to be some changes in how this is hanled in the 3.5 series. This is likely to be due to the fact that the node location functionallity has moved from the object editing screen.
After a quick look at the source code (hint hint :) it appears that the varaible useNodeAssigments must be set to 1 for these variables to be used (it is set to 0 by default).
The following variables must also be set or the placement will fail:
+ MainNodeID
+ SortOrderMap + SortFieldMap
The function to look at is storeNodeAssignments starting at line 226 of kernel/content/node_edit.php
At this point in time I have not tested this functionallity, only looked at the source.
Your explanation of the SortOrderMap and SortFieldMap make a lot of sense and clarify the last little bit I did not understand the first time around.
While I've not used this functionality yet, I believe in it and urge anyone else trying to use it to read the applicable kernel/ source code.
Perform some interactive debugging with tracer bullet output ( echo/print() )and breakpoints ( die() ) with all cache <b>disabled</b> to learn for yourself just how to successfully develop using this functionality.