When I sorted the items for this Sunday's upcoming auction (high to low), it appears that any item that has gotten a bid of over 100.00 uses the 19.5% BP, but anything that is currently UNDER 100.00 so far, has the flat, minimum 19.00 premium added to the bid amount, rather than using the calculated BP percentage.
I looked at about 7 items, all with bids under 100.00 and they all came up the same way. (current bid + 19.00)
And the few items that are currently over 100.00, all have the 19.5% BP used as the calculation.
Edit: Those items that have bids of $97.50 (or above), will use the 19.5% BP figure, since that calculated percentage will be greater than the 19.00 minimum that is added to lower priced posters.
Im thinking it's always been this way. The min. premium fee has just been raised, starting this coming Sunday.