At ECC sum-1, the maximum PIF is 4 (standard, actually at 1x and with calibrated measurement).
Scaling to 32 at sum-8, assumes that the rate is even, when it probably isn't, so a more usual compromise is 16 - though that could still represent an eves 2 across 8 ECC, or a badly out of specification 16 on one.
In many cases, the answer is "it doesn't matter", as it's really only useful if you can tally those results with the actual readability in a PC drive or DVD player.
If a burn scans VERY badly, mountains at the end etc., you can be pretty sure you will have problems with it, but that's about the only constant - it can scan well, and still play badly, or a fairly ugly scan can turn out ok (though it could be rather suspect for archival).
In the end, it's a comparison, not an exact measurement.