G'day fogie,The trouble with the "true flageolet" is that it meant different things at different times. The position (front or back) has little or no effect of tonality ... just playing style.
To me, the "true flageolet" is the type with the "onion dome" top ... with the wind supplied through a tube into an air space - a sort of "balancing chamber" so that the attack is much gentler, the tone sweeter ... but the range shorter since it is very hard to overblow for octaves.
To others ... I did see something about a new "narrow bore" line of Susartos. I haven't seen these, but I have a range of the earlier two bore ...both in tunable and fixed types. My high 'd' is a fair bit smaller than a descant (soprano) recorder ... even with a tuning slide! (and my low 'D' is is BIG ... but not quite as big as an Overton ... or one of my own parallel-bored alloy models.
Regards,
Bob Bolton