I'm a software guy and didn't sleep through my calculus classes! To be honest I was originally a EE major and thought I'd need it.

I switched majors halfway through (and haven't looked back!)
..of course this is all geometry...
The key operating factor to make a skimmer function at removing dissolved organics is water surface contact. We want the most surface area possible. We get the most surface area per volume with smaller bubbles.
Actually here is a rule of them. Assuming bubbles are all spheres, If you half the radius of a sphere, it's volume will be 8 times smaller. So If you can gather together 8 of these smaller bubbles and compare their total volume to the original bubble's volume, it will be the same.
Now the good part: these 8 smaller bubbles will have exactly twice the surface area of the larger bubble.
(
another good one: If you take a bubble and split it in two, you'll get about 25% more surface area out of the two bubbles.)
Surface area = 4 * PI * r^2
Volume = 4 / 3 * PI * r^3
Skip the rest of this post if you don't want to see the math
Heres is the math on the bubble volume:
8 * 4 * PI * (1/2 * r)^3 (eight of the 1/2 radius bubbles)
= 8 * 4 * PI * 1 / 8 * r^3 (Expand the (1/2)^3)
= 4 * PI * r^3 (reduce the 8 * (1/8) = 1)
And that is the formula for the full size bubble.
So the surface area of the half radius bubble is
4 * PI * (1 / 2 * r)^2
= 4 * PI * 1 / 4 * r^2 (expand the (1/2)^2)
= PI * r^2 (combine the coefficients)
take 8 of those:
= 8 * PI * r^2
= 2 * (4 * PI * r^2)
Notice that this is 2 times the original bubble surface area