Shocks on springs actually have more clearange than coilovers because where the wheel sits, its below the perch, so no spring in the way. coilovers the spring comes down past where the perch is on standard strut/spring combo so will foul in more cases than standard (hopefully that made sense).
As for the some wheels of that size fitting and others fouling, NOT ALL WHEELS ARE THE SAME. some 8" wheels with the lip will measure in excess of 8". others a little less. it all depends on the wheel.