Hi, thanks for the detailed reply. I did pretty much like you suggested but have it working on the 1st two clicks instead of the last two otherwise the lever would "escape" down to the 1st position when changing from big to small ring, then need 2 clicks to get back. It works OK now. There was rubbing on one or two sprockets with the Chorus FB FD, but I replaced this with the bike's original Xenon QS FD which has a wider tweaked cage (by a previous owner) and no rubbing at all.

I'm a bit annoyed though - I did as much research as I could on these elusive FB shifters and all said they are "2/3x10 compatible" and you "must use an FB FD". I'm new to Campagnolo stuff (and trying REALLY hard to like it) and didn't know that my Xenon QS FD has the same ratio as the Chorus FB, resulting in purchase of an FD I didn't need.