The "Available Balance" before requesting payment is only an estimate and usually does not correctly reflect the tax withholding calculation.
The correct value, along with all the detailed information, is only shown in the final report once you request your payment. So it is normal to see a discrepancy before request your payment.
If you are a corporation, it is best to fill out all the tax information with the appropriate specialist, usually a company accountant or get advice from people who know the tax laws of the state where you have your company.
If it is better to be a company or an individual, it is also something that is better to get advice from someone who knows the laws of your state.
In my limited knowledge, the normal thing for a person is that Itch withholds a tax that is given to the IRS and then, when you file your return, it is calculated whether the IRS returns part of that withholding, but this is my experience as a person, do not take it as advice, especially if you are a company.