SSA taxes are calculated on the gross not on the net after insurance and 401k. Take a look at last year’s W2 and you will see that SSA wages in box 3 is higher than wages in box 1. Income tax is calculated on box 1 but FICA is calculated on box 3.
Here is a sample W2 to see what I am talking about.
http://www.irs.gov/pub/irs-pdf/fw2.pdf
As to whether you can force an employer to not count medical insurance as medical retroactively, I have no idea. I'd be willing to bet that he'd have to recharacterize all employees' paychecks and that is extremely unlikely to happen.
On this very w-2 statement the amount in Box 1 is the same as in box 3.
Neither is the gross wage.
In the bottom right area there are two different values.
They are $5400 different apart, the amount of the medical payments.
Both box 1 and 3 are the lesser amount, the reported wages.
So I cannot agree with an assertion you make.
That link only hangs for me, can you post the content of that irs pdf page, sample?
Thanks.