Hi! I have 4 cobs for a total of 200W in a 80x40 cm and it's not too much.
What is the color of the led? I use a 3000k from Bridgelux.
I think 100 cm is too far from the lamp if you are not using any kind of reflector.
The limited stretch is more about 24h, some genetics will bush like crazy!
Also cold temperature and dry air in vegetative stage will make them short.
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