Trigger phrases are something like:

"The {Subject_1} is on all fours."

"{Subject_2} is at {Subject_1 Pronoun} rear pressing {Subject_2 pronoun} crotch against {Subject_1}"

This model can make some funny combos!

This is actually not particularly good at the sex part. I debated calling this "From Behind", but someone might be able to figure it out.

Things to avoid (maybe):

Saying "behind" means in relationship with the viewer, So the {subject_1} could be viewed from the side, and the {subject_2} is behind them, meaning to their far side and not behind the person's rear. Maybe that's desirable for you. I have a statue example that shows what I mean.

Boring notes about training:

I'm finding that trigger words don't mean a whole lot with FLUX. While I did train a trigger word, I did not include it in any of my prompts. The trained trigger is doggystyle_sex . Just be descriptive of the image and Flux seems smart enough to understand what it's supposed to look like.