One thing is wright, you can never tell what the end yield will be.. but that is mostly due to watering, food, pests, humidity, soil , strains, breeds i mean i could go on. one major stress stunt can change your yield.
35 years growing about half indoors. What i and others have noticed is:
Exp grower... about 1gram pr watt. could be a little more or less but then it depends on soil or not.
I have always come right around that. Less plants bigger and tighter buds.. have done some major ops (but of course there were major lights with a lot of watts). but that system is what we used for a base for numbers.
Shit some of the new strains and breeds being crossed now a days...maybe one day i can get the weight i get from outside on the inside
This is just and old 50 year stoner opion though.