The total number of guest-worker visas would be able to climb in any year to a cap of 200, 000, but any number above 20, 000 would require passing a complex bureaucratic formula.
In these circumstances, I believe it makes good political sense to keep it simple and just guarantee that no worker with personal accounts will get less in total benefits than Social Security promises today, rather than try to defend a complicated, more limited guarantee.
This calculation establishes the total cost that employers are willing to incur to employ that worker, and the employer is indifferent to the composition of the pay package comprised of wages, benefits, and payroll taxes.