A healthy Hayward would be flashing in the high post. But depending on him while injured/recovering/rusty seems perilous. Smart should be the next choice for that role. Smart has 3 quick choices to make once he gets the ball: draw/dish, attack the rim or shoot a 15'.The problem with having a player flash to the FT line is that unless the player is accustomed to having the ball in a high post position they are being set up to fail. A zone defense should invite this pass and prepare to swarm the moment he puts the ball on the floor. It takes a quick reaction and Jaylen doesn’t seem to be the right guy for this as his strength is in iso or transition. Theis or Kanter would be the ones who could handle this spot and maybe Hayward as he is a quick enough decision maker to handle this as well.
Setting screens up top or passing around the perimeter plays into the hands of the zone, it drains the shot clock and gives the zone time to reset.
Credit to Miami for going strong/long at the top of the zone with Crowder/DJJ/Butler, they have done a good job disrupting penetration & kick-outs.
The good news is once the Celtics figure it out, you can run the same play continuously since you know where the defense will be every trip down. The bad news is Spolestra knows this and will adjust immediately out of it once the C's get any kind of rhythm.
A well-executed zone probably screws up the Celtics more than most since they use their BIG primarily to set screens for their more efficient offensive players. Having him (Theis/Kanter/TL) flash at the high post to distribute or shoot isn't ideal. Grant could probably handle it, but you're asking a rookie in a high-pressure game dictate the Celtics offense.