"Yet the IRS disallowed EIP #1 and not EIP #2"

Did you take into consideration the payments they received? This is not just an issue of Credits. The Credits were paid in out in advance, as much as possible, and the 1040 form is the reconciliation of entitlement to money already received, based on eligibility.

"Since the phaseouts are different, shouldn't the reduction factor be 2 diffeten percentages?"

These are separate provisions, and whatever is the same or different between them is moot. You do the math for each, and compare to the payments of each, as separate.