I wouldn’t be concerned about lowering or removing the SBB at all. Leaving in the top position help keep your bees from getting under the screen. I just leave mine in. Only time I remove is to check for varroa mites or cleaning the junk off it. Others might have other thots n ideas but I just leave mine alone ! Were still chilly up here at times but several runs of 80’s thus far which is way above our normals of 50’s n 60’s. Rainy n gray today in the low 50’s.
It depends on your personal beekeeping philosophy. I have been told by people that I trust(both here and in the local club I am a member of) to leave the board in the top position all year round. I have had several days over 110F in the sun already this year and I have seen no evidence that they are having trouble keeping the hive ventilated, no bearding etc.
So that would be my recommendation though I am still new to having a hive as well.
When you want to trap SHB or other pests. If your bees haven’t drawn much comb yet, that won’t be a problem, I would leave it in the upper position. If you do move it to the lower position, the idea is that now the bees can’t reach it (unless you have a faulty mesh in your SBB) and you can coat it with Vaseline, cooking spray or sprinkled insecticidal diatomaceous earth to trap and kill what falls on it.
When you harvest, it needs to be clean and free of anything noxious. You then put it back in the upper slot so that the bees can reach it again to lick off any spilled honey. That keeps robbers and ants away from the hive.
If you are going to leave the board in, it doesn’t really matter whether they are over open air or not. If you are going to take it out completely, you probably want a way for debris to be able to fall to the ground.