In view of what you've said, the upright does seem far enough left to allow an F...also there does appear to be a small triangle that could represent the end serif of the top bar of an F, plus a faint crease where the lower crossbar might be? Maybe another block, as in the 1700 NO STOP after DEI?? This doesn't mean that it 'isn't' the IRA for FRA that's described in Spink's, of course, just that Spink's may not yet have resolved for themselves the issue of the genuine existence of the variety or not, or whether it is instead a block that produced a run of I for F looking coins! It's a great period, and great looking coins, especially the halfcrowns! That's why I am sceptical about the so called GVLIEIMVS coins. Blocked lower bar Ls with the upright too far left is the order of the day, but that's because people see what they want to see and we all know a listed rarity commands a higher price, just like all those proofs on eBay which appears to have a monopoly.