the IRS is not supposed to grant an installment agreement unless and until you are in full compliance, meaning that all tax returns have been filed. see this link
https://forst.tax/installment-agreement/
you may be right about not being required to make a large down payment on an IA. it's been years since I helped a client with unpaid taxes and at that time the IRS wanted the largest down payment the taxpayer could afford (taking into account what he needed to provide for himself) this included financial disclosure.
here's some more
https://www.thebalance.com/installment-agreements-3193406
