my 1st plant got like ~3.3 ounces. used 400W of light towards the end. it was 1.5 feet tall when flowered but incredibly stretched (only 4-6 leaves), having nearly died right before hand (good 'ol newb gardening).
its really all about:1) genetics 2) light coverage (lumen/area... proximity 1-3") 3) nutes. feed and water well, keep lots of light close to the plant, and get some air to it.
best of luck