Gulp! That still doesn't me. Sorry!
Am I overthinking this and the flex temp is just a co-efficient reflecting the environment which happens to be a temperature by convention (perhaps because that was how they first looked at it when the technology was being developed)? It could equally be assumed runway length or inside leg measurement etc?
A bit like how the co-efficient of lift is really just the last figure to make the equation work as empirically demonstrated by the airfoil's performance at different AoA, flap settings etc. once you've entered the square of the speed, clean wing area and air density ?
Thx
M63