@EvilScotsman i had them at 2 foot for the first few weeks then slowly lowered.
The cobs are an expensise outlay at around £120 each although you can build them cheaper yourself (i picked up a bargain on ebay about 50 quid each)
But i was running 600w hps and at 14p per kwh that costs 8.4p per hour £2.01p per day at 24h lights on.
Over a standard 80 day grow for me that was costing £160.80
Running 200w of cobs costs only £53.60 per grow so saving nearly the price of a cob per grow...
Holy fuck what a stoned rant point is they pay for themselves after only 1 year