squirrel cage fan run length

Im getting into a legal grow and want to use all my 6Inch CoolTubes. I found this a long time ago online but can't seem to find it anymore...

Anyone know the total length a 6inch squirrel cage fan is good for before you need another inline fan to push air through?

I sort of remember it being like every 4 - 6 lights you'd need a new inline fan?

Im sure theres a formula for this I'd love to have but again can't find this online.

Thank you!

cool tubes sucks but if u have to use due to ac restrictions fair. Yea only 4 but I find it still sucks. Personal experience . Light distribution creates a bow effect. Tall plants get more light outside than the ones directly under

Thanks! So 4 lights, if spaced @ 5sq feet apart then every 20 / 25ft or so put a inline fan?

I love cooltubes why you hate because of the bow affect? I've seen a bit of this but not sure why more light would go outside than downwards. I know that open hoods have more lumens but other than that cooltubes should be better than regular hoods for air movement...