The government now has a tool that supposedly tells you where your tax money is going. You can try it here. I did not have my own tax data handy, so I used the generic family with $80 K in income.
In my receipt, I cannot find any line item for the main Social Security program, OASDI. Under "job and family security," there is a line item for retirement benefits for Federal workers (in fact, this is the largest item in the category). But nothing for retirement benefits under Social Security, as far as I can tell.
So I do not understand the calculation. Maybe it's because of the Social Security trust fund somehow. Until I understand what is going on, I don't think it makes sense for me to try to comment.