It's no secret that a large part of the fighting forces are made of DPR and LPR fighters. Up until yesterday Russians were not overtly fighting in Donbass, but it seems to day the armies of DPR has reached the border and joined with Russian forces, which presumably came up from south.

None of this changes the original point - regardless of where RF is fighting, they are brutally successful and precise in their targets. Slow, yes, because of reducing civilian casualties, but not inept.