forced induction question

[tcodi]

Ok, I understand the compression limits of certain octane leveled fuels. If I put a blower on a motor:
Standard Atm. Pressure is about 14 psi we'll say
If I set up a blower pushing 7psi of boost, this brings us up to 21 psi. Everyone says if you run forced induction you have to lower compression ratio, which makes perfect sense. But it seems they say to lower it to around 7 or 8.
Wouldn't the compression have to be lowered by the same proportion that boost is added?
What I mean is, if I can run 11:1 maximum on 92 octane, and I go from natural asp. (14psi) up to 7 psi boost, then that's an increase in the amount of air inducted of 1.5 times. So shouldn't I adjust my compression by the inverse; 11/1.5 = 7.3333
That way if I start with 7.33:1 static, then the compression should come out to 11:1 if I push 50% more air in the cylinder.
How the heck do guys run 14psi boost, wouldn't you have to cut static comp. down to 5:1. How do you find heads with CC's that big?