A question about Standard deviation

[Girchuck]

I looked at my 6-max SD, it is about 17BB/100 hands. Other posters report similar numbers (I saw 15-20BB/100)

Now what if I calculate SD/2 hands. The maximum I can win in a hand is 60BB, the maximum I can lose in a hand is 12BB.
So, a maximum SD in 2 hands would be 72BB/2 hands, right?
Now, to calculate maximum SD/100 hands, I would take max SD/2 hands and divide it by square root of 50, right?
If this is right, I come up with a maximum SD of less than 11BB/100. But it is less than my actual SD of 17BB/100. How can this be? Where did I make an error?