Understanding ACA MAGI and Roth Conversion Amount

I've been mapping Roth Conversions while still being cognizant of ACA FPL limits. I've told Pralana to assume ACA if eligible.

In the tool, I followed the advice to let it run its own Roth conversion optimization first, before setting any limits. That produced what seems like a fairly optimal sequence, converting up to the top of the 10% bracket, or $23,850 before any deductions, in today's dollars.

When I click on Metric MRI for my conversion amount it shows me the unused deductions/exemptions of $23,864 (future dollars) plus the top of the 10% bracket at $26,062 (future dollars) are added together to reach $49,926 (future dollars) in total conversions. Since deductions/exemptions can be applied against "income" from Roth conversions, that seems all well and good to get AGI back down to the top of the 10% tax bracket in that step.

At the same time, the conversion result spreadsheet shows me I'm still getting substantial ACA subsidies all the way over on the right of $19,321 (today's dollars) in the first year. Using today's FPL of $21,150 for a couple, at my total conversion amount of $49,407 (today's dollars), we'd be at 233% of FPL before deductions, which as I understand are added back in for ACA MAGI. (We also will have a contribution to an HSA of $9,343 (future dollars) in that year, which is allowed to be deducted from ACA MAGI and thus increase the overall amount of conversion headroom.)

This all makes sense to me, since ACA subsidies don't completely phase out until 400% of FPL. But I am still surprised at the relatively high level of ACA subsidies for that conversion amount compared to FPL levels.

Can someone with a better understanding than I of ACA subsidy cliffs provide insight as to whether these numbers make sense to them?