oh also good reading
https://www.motortrend.com/how-to/17...-gotten-wrong/
Preload will change ride height without changing the ride quality/stiffness and also without changing the shock body length. Which means you'll have the same suspension travel.
Whereas adjusting the shock mount will change the length of the shock and will change the wheels position at full compression and full droop.
With that in mind don't the divorced rear springs on a BC BR come with an adjustable perch? I think most divorced setups come with that. You can adjust that to adjust preload and subsequently ride height without changing the shock body length. I don't know what is an "acceptable" amount of preload but I assume if you are adding too much preload at some point you will need to extend the shock body length via the adjustable base. And possibly get longer springs like the guy in this thread below:
EDIT: Looks like they do come with adjustable perch?
Bc racing br coilovers