I think he stays with 2 bigs. It's working right now. The only reason they would go back to White starting is if Joe thought their spacing wasn't good enough to generate offense, to the point where it would be a net gain to have a smaller lineup that can play a five-out offense.
But if you look at the numbers, White has tailed off somewhat from his great form from January. He's still solid, and obviously he's a great perimeter defender and 2nd team All-NBA, but he's not quite as irresistible as he was when people were saying Joe should drop Marcus from the starting lineup and play him. Obviously his minutes are down, so his raw numbers are down, but his efficiency is down as well.
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Obviously a lot of it can change after the Game 1 experience. How Miami play us could influence the lineup. But to me the starting lineup just sets the tone, it's who plays throughout the game and who finishes that matters, and I think we'll see a lot more of Rob than we have been, whether he starts or not.
In any case, Derrick is the ultimate team guy:
“I’m not entitled to that spot,” he said. “If it’s what’s best for the team, we go with that. Rob’s a great player, so I was with it ... I was all for it.”
https://www.msn.com/en-us/sports/other/derrick-white-has-maintained-his-focus-since-being-replaced-in-the-celtics-starting-lineup-i-m-not-entitled-to-that-spot/ar-AA1b9oYJ