Ok, I got that... I tried out some stuff in script.rc but I didn't get any exciting results. I tried to add a line here:

*Script label ColumnFull_lbl
; if the column icon count is now 3, then a new column was created for this
; icon, so:
; - taskbar needs to be shrunk to free room for the new column
; - new column contains 1 icon, so column icon count is set to 1
*Script exec |TaskbarShrink 18 -1
*Script exec |VarSet IconsInColumn 1
HERE
;*Script exec |Alert "column full, IconsInColumn = %{IconsInColumn}, IconCount = %{IconCount}"
*Script ~bang

I tried to put:
*Script exec |VarSet AmpX $AmpX-18$
and also:
*Script exec |VarAdd AmpX -18

But nothing happened... Any ideas?