Watching the replay, one play with RobW stood out to me followed by several plays by GrantW.
In the 1st quarter, Miami put up a shot from the left wing, which missed. RobW had the weak side and stood there watching the shot assuming he would simply jump and snatch the rebound (great athlete, great length, etc.). Trouble was that Adebayo came up right behind Rob on the baseline, easily got inside position, got the offensive board, the putback layup and foul from behind by Rob.
GrantW subs in for Rob a few minutes later and proceeds to put his very stout body (decent athlete, not much length) into Adebayo every single time a shot went up. Grant didn't get every rebound, other Celtics rebounded some in the cleared out space, but Adebayo had one more offensive rebound the rest of the night. It was beautiful watching Grant focus on what he does well to help the team. Looked like that every Miami shot that went up, Grant was putting a body on somebody, over and over.
I realize that blocking out on rebounds is not emphasized in the pros, you see it some, but not consistently. The players are so big and athletic, they just go get the ball without even looking for someone to put a body on first. You see it all the time and it often results in offensive rebounds by the opponent. Just hope Rob was paying attention and that Ime will make a point of it during film sessions. Rob's improvement has been great to watch and is one reason the Celtics have been so good this season. Keep working.