Springs determine ride height
You won't be that low that you are running on the bump stops. I would advise you cut down your bumstops by an inch or so anyways.
Did the coilovers not come with the rear shocks?
Another thing you can do is remove the rear adjuster collar so you are running with the spring only but upon jacking the car up the spring can pop out, not really ideal or very safe but i have done it previously back in the day
Or if you screw the adjuster collar ring right off that will give you an extra 5-10mm upon what you have right now