I'm sure there's not a constant ratio. It's actually going to be a function of veg time and will also be highly strain dependent as far as the total height of the plant achieved during stretching in the flowering phase. Most sativa's can get pretty tall. You can limit the height of a plant through the container size, as an example, a plant in an 25 gallon container will get much larger than one in a 7 gallon container.

What I have noticed that seems fairly constant is that I typically get yield numbers similar to container size. I like using Pro-Can pots (standard nursery containers) and with a #2 I always get about 2 oz per plant dried, with a #5, I get about 5 oz per plant.. Seems to be similar on the #7's I use now.

Peace, Farmer Rich