Without suggesting that the following is the final word on the subject (I hope it’s not. I hope someone proves me wrong), I think you understand things correctly.

Maybe 4 years ago I set out to find all the ways to create “pseudo-spillover” with the H9 (which does not have real spillover). The trick was to find a way to throttle the input to the effect (most of the mix controls manipulate the effect output, not the input) . In Space, all I could find was the A/B mix control in DualVerb just as you mention.

I also found this ability in H9 algos UltraTap and in PitchFuzz. FWIW I have attached H9 preset images for those. In PitchFuzz, I feel like I’m trying to outsmart the algo to pull this off. By contrast, I feel that UltraTap is the best H9 algo for this b/c this feature appears to be specifically/intentionally included in the algo. I have also attached an UltraTap flow chart showing why: the Chopper can be controlled by an expression pedal upstream of the Taps Engine. Other than in DualVerb, I’m not aware of any Space algo that does anything similar to this.

Hope that helps.
~Tony