I’ve used as many as four bricks at a time for heat sinks. Two below and two above the not quite defrosted turkey breast that I was smoking. (There was plenty of space in my six rack.) Because it was cold, windy, and rainy, and I still had some ice crystals in the cavity area of the bird, I preheated the bricks in a 400 degree oven before transferring the bricks to the smoker.
If you’ve got the space, I think that using heat sinks speeds along the cooking part of the smoking process. For me, heat sinks are part of my smoking routine. Regardless of the outside temp.