Pre conditioning the air before the intake will help. I always heat/cool, hum/dehum the ante room the tents sit in and I also watch/control the zone in the basement that my ante room breathes from. Makes it easy, (outside of Aug/July) to keep a tighter range in the tents themselves.

Im glad you got it locked down on the right track. Like i said lots of this stuff breaks down to figuring it out. Problem is we all do it where we rely on our equipment only to find its our equipment that is letting us down.