As far as I can tell the width of a column when autosizing of columns is false is a faction of 1.5 with an offset of three units.

When the search dialog of a cdbCjgridPromptList, is created it retreives the piwidth of the column to help determine the width of the search dialog.

If the computed width of the search dialog exceeds the containing object ie the grid width the popup relocates to location 2 2.

To ensure 2 2 is never used I think the second code line below needs added to the Request_Search method of the cdbCjgridPromptList


Code:
 
Get piWidth of hoCol to iWidth
Move ((iWidth + 3) * 10/15) to iWidth < add this
I found this when using a single column prompt list which did not have other columns which exceeded the above formula.

This is easily recreated by making a single column prompt list.