I have always run +35 to +38 for FOB at these type of shows with my 4022's.
+40 for taper section @ Phish.
+25 with DPA's sounds really low to me, I have never had to run that low even at the loudest shows. Lowest I have ever run is +30 or so, never gone below that. Maybe your 4021's are more sensitive than my 22's?
Hope this helps, pull some sickies! Team DPA rox