My 2 cents, unless you are into all out big buck racing, you probably are not going to see any difference between flat flooring and using scales. Also using the scale or lever arm lift you still need a level surface to correctly compare the wt of each corner. You would be lucky if 1 out of a 1000 cement floors would even come close to being level. 20yrs ago it cost $2.5k just to level a pad 24' x 8' to within an 1/8" . That's just to level and not the cost of matl.
Here a photo my corner wt scale set-up, and a typical leveling block. My pad locations with a leveling block are all within 1mm tolerance. This set-up reproduced repeatable corner wts within a 3 lb limit. Now after going through all the BS to get an accurate corner wt, I could not tell any difference.
IMHO close is close enough when doing corner wts on a road going Seven. For a road car, I would just use the simple flat floor technique. That's really all you need.
Davew