Great observation: anything added to the smoking chamber will act as a heat sink. When adding something cool to a hot place, and without any adjustments, the temperatures will try to normalize. When I light my smoker, I set the thing higher than the temp I try to maintain. For one thing, I don't think it hurts a bit to be on the hot side right out of the gate. Once you see the temperature normalize, after about 30 minutes, make adjustments to your smoker to hold the temperature you are trying to hold.
It all depends on your particular kind of smoker and what you are trying to cook, for the amount to go over, but I suggest about 30 degrees.
Also, make sure whatever you are cooking is room temperature. If it comes straight out of the fridge, it will take longer for the temperature to normalize. I pull the meat out of the fridge before starting my fire. I let it run for about an hour to get a good even burn, then add the meat. By that time, the meat has reached a good temperature and hasn't been in room temperature long enough to be considered "danger zone" meat.
Hope this helps.