Overlays in make.conf with poudriere

Hello,

i am using poudriere-devel (3.3.99.20211130) with Overlays for a while. 
This happens via the -O option in poudriere bulk and works fine.
I want to use Overlays directly via the 
/usr/local/etc/poudriere.d/make.conf so the overlay is applied in every 
bulk run without explicitly enabling it.
I tried these in make.conf but that has no effect:
OVERLAYS+= dss_overlay
and
OVERLAYS+= /home/poudriere/ports/dss_overlay
bsd.port.mk also has this in it:
bsd.port.mk:OVERLAYS?=
Maybe i am missing something obvious, but i dont know whats wrong there.

Sincerely,

Henrik Rosenke