Sure enough, it's not that simple. I left leg length at 100 when I tried to figure out the height function. There's definitely more than one parameter to that function, because when I ran the leg length slider to zero (i.e. minimum) as well as height, I ended up 4'7" tall.
So... should I try to figure it out myself, or take the easy way out and go looking to see whether someone has already documented it? :) I think I'll go looking.
I should build a simple grid on a sheet of plywood for this sort of thing, but instead I took a picture from what I hope is a good POV for reasonably accurate measurement, and used the convenient cursor position reporting in the GIMP to try to measure some things.
My height turned out to be 1050 pixels in the image, which maps to 86", since I'm 7'2" in my stocking feet (in SL!).
One can look up world record leg lengths, but it's harder to find out just what they're measuring. (The Guinness World Records web site gives no email address on their contact info page, probably figuring that having to actually write on paper and buy a stamp will filter out a lot of the riff-raff.) From some pictures and one web site for a model (Dji Dieng), it appears that what's measured is the "outseam," the distance from ankle to where the waistline of one's trousers would be. Of course, differing styles make that last bit kind of arbitrary, but I did my best, and think that my outseam comes to about 670 pixels, which maps to 55" (or around 140 cm in a rational system of measures), and inseam to 570 pixels, i.e. 47" (closer to 119 cm than 120 cm... BTW, those who argue that the metric system lacks the handy bits for estimation that the imperial system, based on lengths of random kings' feet or arms or whatever, supposedly has, should note that 10 cm is a hair under four inches, the "hand" that horse heights are measured in).
[UPDATE: I decided to trade in a little neck length for added leg length. Not much, though.]