Bulls coach Jake White said that the extra travel the South African sides have to do in the URC is putting them at a disadvantage.
After going down to Connacht at the weekend, the Sharks have lost all five of their URC clashes this season.
Munster ground out a hard-fought 10-3 victory over the Stormers at a drenched Thomond Park after academy lock Edwing Edogbo's second try in five.
Fly-half JJ Hanrahan's second-half penalty edged Connacht to an outstanding 13-12 United Rugby Championship victory over the Sharks in Durban.
Ulster came from behind to beat the Lions 24-17 at a windswept Kingspan Stadium scoring three tries to the visitors' two in game which was in the balance throughout.
Edinburgh claimed a fourth victory from five starts in the United Rugby Championship (URC) when they battled to a 31-23 victory against the Bulls at Hive Stadium.