If it were me I would run like this.
Filter>fan>cooltube>cooltube>into larger duct> out through window. The arrows been the air flow direction.
There should be enough airflow just passively coming into the tent and the room with that sized tent and fan.
The other reason I asked to see pics was for thermometer placement. You have it hung in direct light, The light from the HPS will heat it up. Try hanging it above the light line so its not getting warmed by the lamps. The air temp is the key temp to keep lower, the plants can handle higher radiant temps. But to take air temp accurately it should be just above where the light line is.
I gave away my 1mx1m without ever using it and two of my cooltubes to my mate, he ran them vertical in the way I described. The good thing about cooltubes is you can push air through them without causing any turbulence and loss of pressure. The bad thing about them is the loss of light through the glass and the foot print been smaller, you wont have those problems though ey with 2x400w
Anyhow, shift your thermometer and see how temps look, if that's enough to sort em out then no need to chuff about with changing it all round.
Take it easy.