sometimes enlargers have a secondary condenser, or a different configuration for different format films.
i have a little durst m601 and you are supposed to change the square condensers when doing 6x6,
and with the omega d3v ( sort of ) there is a condenser i am supposed to slide under the lamp house
and above the big condenser lenses ... maybe someone with the same one or knowledge of yours
can comment about the max. format it is capable of taking, without fall off ( like you are getting ).
( i know nothing about besslers )
nice print btw !