Height doesn't delineate amount of yield. Genetics are a determining factor, coupled with lighting, nutrients, medium, atmosphere, humidity, temperature, CO2 levels, etc.
Add in nutrient lockouts, burns, stresses, transplanting, pruning, etc and all that effects yield.
This equates to mroe than just how high you grow them in the vegetative stage.
More than heigh, I grow until they are sexually mature in their veg stage(showing pre-flowers or alternating branches). This is typically 45-60 days depending on strain, from seed.
If I were to answer your questio directly, I would say grow veg until atleast 8-12".