I would say it is a clear cut answer, in line with Jim's reasoning.
Simulator training counts as 'duty', therefore the limits on 'duty' agreed with the CAA (etc) for the FTL scheme remain applicable, along with the required rest days and periods preceeding an FDP.
So, I would say that Geoff's 12 day stretch would not be acceptable to a CAP371 operator. Equally, there is no constraint on whether a mixed simulator and flying FDP has the sim session prior to or subsequent to the flying activity (though you as an operator may place such a constraint.)
The bottom line is that the FTL scheme is for
The Avoidance of Fatigue In Aircrews
and therefore following a period of simulator training (or indeed any activity of duty) the crew should be in a fit state to re-commence normal line flying with members OF THE PUBLIC.