T5s can work wonderful for flower.
Here are my flowering ladies under t5 lighting.
#3 under 2' 4 bulbs
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The beast clone under 2' 12 bulbs
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Your t5 fixture is no slouch.
But you need to keep it 2-3" above the canopy for best results.
You will also want to train your girls more with a longer veg.
With t5 lighting you want a nice even canopy with many tops. That way you will focus most of the plant growth up top where the best light is.
This will help you with size and yield.
t5 lighting makes better flowers than people expect.
You Just need practice that's all :)