Hi Phil, what do you weigh/which sail sizes? Generally we have fairly "small" front fins and a bit bigger sides on most of the FW TE Tri Fin setups - so the 105 TE has a MFC TF set - 21cm centre, side fin 12cm. So I would tend to stick a bit closer to that and go maybe for a 23centre/12cm sides.
if however you prefer a bigger centre fin, then you can try something like 24/25 centre and smaller sides in 10 or 11cm?
This would be the bigger set:
and the more standard version as per above which is supplied with the smaller TE´s is the MFC TF set - but I just checked that and it only goes to 19cm in PowerBox as an accessory fin.
But maybe some other users here also have some good tips for Thruster sets?