Yeh Field length limit TOW is the lowest of the ASD limit TOW (accelerate stop distance) and TOD limit TOW (Takeoff distance)
Also thats not mentioned is the Obstacle Clearance Limit TOW to clear all obstacles with the required margin.
I think i know why my FPPM now supplys charts for;
Improved Climb Field Length Limit
And;
Improved Climb Tire Speed Limit
As any of these can be the limiting factor on the ground for the Improved climb? I stand to be corrected. If anyone would like to see the FPPM and those charts let me know. It may help my confusion..