I don't consider t5s a real vegg arrangement, jus a place to make roots. I get the girth stocky with the big lights for a few weeks before flowering holmes
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As long as you don't end up with dry spots it should be fine.
You don't really need much runoff at all.
Just enough to make sure they get wet.
Did you see FBN's trays?
check your ph calibration
maybe your lights are too close?
That can be common when running c02. What are your c02 levels at? When you mix your nutrients, use the 6/9 ratio but use 10-20% less water than you normally do.
Also, you don't need 20% run-off. 5-10% is fine with 6/9 and many have run it with no run-off.