I recently picked up D-Day by Antony Beevor again and chapter 15 covering the end of June mentions Colonel Vassilievsky being bought to the HQ of the 7th Armoured Division and expressing the view that the British advance was very slow. A British officer asked him to show on a map of the eastern front where his own division was fighting. "It transpired there were nine German divisions on that sector, which was over 600 miles long. The British pointed out that they were facing ten divisions, including six panzer divisions, along a front of only sixty-two miles." So at least at the division level there were Red Army officers liaising.