The zorder in a form is controlled by the record position of the controls in the SCX table. I did a simple test of a form that I had multiple overlapping objects. If I open the form before any change and determine an object name on top, then close and USE the scx file (open as a table) and find the record for the object (in my case the record number was 98). Then close and modify the form, select the control, 'send to back' and save. Then reopen as a table, now the control's record number is 4 (the first control in the form). Close the table, re-modify the form, select the control and 'send to front' and save. Now the record number is 109 (last object record in table).

From this the objects in the table are placed on the form sequentially as read; the zorder is derived by the object order in the file.

You would have to compare the objects for overlapping and then determine the zorder value (0,1) based on the sequence. The 'middle' ones would not have zorder by (0,1) -- you would need to come up with your own method of keeping track of the 'stack'. You could do placement by executing a loop with the bottom first and for each control execute zorder(0) (send to top) -- this should restore the stacked sequence.