If this is getting too complicated, maybe you should just get on the turbo, progressively increase the watts every minute until you can't carry on any more, then take 75% of your best minute power and use that as your FTP.
@Acliff started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
If this is getting too complicated, maybe you should just get on the turbo, progressively increase the watts every minute until you can't carry on any more, then take 75% of your best minute power and use that as your FTP.