Condensing: behaviour of stems


I am trying to make a condensed score. But with Trombone 1 & 2 some strange behaviours accur.

Please look at the following slices:
Slice 7.png
Here you can see, the first notes have separat stems the others don’t have those.
Slice 8.png
Here you can see the same notes eight bars later. The difference between this two examples is, that in the first example the first voice has an upbeat to the f on the one (this may explain the behaviour). But:
Slice 9.png
In this example nobody has an upbeat and both voices have separate stems.

So, I have tried several combinations of condensing rules in the notation options, but nothing has an effect.

What I want to achieve is that both voices have separat stems all the time. Is there any possibility?

Thanks in advance!

You can set a condensing change manually to keep voices separate in Layout Options > Players > Condensing.

Ordinarily condensing works phrase by phrase. Dorico considers rests as an indication of separation into a new phrase. That would explain Slice 7. The explanation for Slice 9 might depend on what has happened before or after the notes you show.

If you want a manual condensing change to force them into separate voices throughout, instructions are here.