Boston Celtics head coach Brad Stevens has thought just a little bit about changing his starting lineup. “Every minute of every day,” he said. It’s one question that keeps Stevens awake at night. He knows the frontcourt duo of Kris Humphries and Brandon Bass has bled points all season. He knows the bench has looked good recently, sometimes even great. But with a flawed team that has four power forwards, zero centers (sorry, Joel Anthony) and no obvious combinations, Stevens doesn’t know if there’s a solution. Though he did not believe the starters performed poorly Friday against Toronto, he would like more from the unit. But he also does not want to disrupt the bench’s obvious rhythm. “It’s why you think about it all the time,” Stevens said. “Because to me there’s not a clear-cut answer.” Maximizing lineups has been difficult all season; in addition to a lack of elite talent, the Celtics have parity at almost every position, especially in the frontcourt. Stevens said he has “considered changes” on the perimeter, but thinks Rajon Rondo, Avery Bradley and Jeff Green have not spent enough time together on the court. If a tweak does come, then, expect it to be on the interior. “It’s a great puzzle right now for us,” Stevens said Saturday afternoon before a walkthrough. “But those four (Bass, Humphries, Kelly Olynyk and Jared Sullinger) are all good basketball players. That’s one thing that you have to keep in mind. And they can impact a team positively. They may not be the best complements for each other when they’re on the court, but they’ve had their moments.”