Finally tracked this issue down and now have Fire & Ice working in 2.20 (the beta will be available in the next day or so). It turned out to be a combination of two bugs in MiscOp and a timing check done by the protection to ensure the last disc read took a certain time. The later was easily resolved as sectors can be marked as slow (read at floppy speed), however this highlighted a third issue where ADFFS wasn't taking account of the current ADFS retry setting.Fire & Ice fails the protection check, if not run from the Harddisc
The two bugs in MiscOp we're causing the discsig to be corrupt. I'm surprised they didn't show up sooner, it was pure luck that F format disc detection was working.