4" inline 6"ducting?

I've searched and can't find a good answer maybe just not asking google right .. Anyways

I have a aircooled hood with a 6" flange and a 4" inline fan 200cfm and I'm trying to figure out how to connect them
should I just use one 6 to 4 reducer to the intake of the fan and 4" out the exhaust

or what would be the pros and cons of using a 6 to 4 to the fan intake as I said before and then a 4 to 6 with 6 ducting out the exhaust ?

space is only 30 cubic ft
400 watt hps aircooled hood
the fan will be pulling air through the hood not pushing

also I want to put a 6" filter directly on the intake of the hood reflector so i can make passive intakes around my box to cool the light and scrub the box to eliminate needing two fans and all that duct does anyone see a problem with that ?

4 to 6 is fine, bigger concern is you have only 400w for 30 sqft. In 30 sqft you should be running at least 3x that.

maybe o said that wronng my box is 3ft long 2ft wide 5 ft tall ? Yeah I've been looking at so much cfm stuff I got turned around the box is 30 cubic feet which is more relative I think lol

fan is a bit on the large size for that grow space. I'd invest in a decent speed controller so you can dial it down just right.

i ran a 6" scrubber- 6" cool tube-6 feet of 4" flex duct-4" inline fan in a 2'x4' tent and was great! i had 400 watt light, also - that could be scary close to the tops!!