How do I know upfront how much rent Section 8 will approve?

[April Adams]

Section 8 (S8) can pay $1900 for a 1bedroom. So, I ask for $1900. However, the amount was reduced to what the S8 applicant can afford. Which turned out to be $1843. Apparently, the rent is actually based upon the S8 applicant's income. And although I am asking the full payment, I cannot get it, unless I chose another S8 applicant. Has anyone heard of S8 offering less than the payment standard because the S8 applicant cannot afford it? It took nearly a week to find out I would be losing out on $57 a month. I feel forced to accept $1843. How can I know beforehand? How do I know upfront how much rent can the tenant afford?