Which blend mode emulates negative film double exposure most faithfully?

Trying to reproduce the creative effect of exposing negative/reversal film multiple times when post-processing my DNGs. There are many possible blending modes available in digital processing workflow, but I don’t need all that control—essentially, I just want to perform an action that combines two exposures the way negative film would, nothing more.

Following the physics of it, what would be the mode that mimics negative film? Intuitively I think it should be additive, or is it more complicated than that? At what stage should the combination be done, intuitively I guess scene-referred data is ideal but maybe not?

Addendum: here’s an outtake from my many experiments, not to be taken as a reference of course (I don’t remember which blending mode I used here but it’s probably irrelevant, I vaguely recall I mistakenly blended only YUV luma components anyway).