DB01 double slipper clutch possible problem

[e-JP]

I have one on my DB01.

I have a hard time to get some power on the rear wheels.
When I test on the bench all seems right and diffs are tight. But on the track all the power (not really all but maybe 70%-80%) is on the front wheels, so it's like driving a front 2wd.
I have rebuilded the front and rear diffs (according the procedure found somewhere in this forum), double checked the slipper clutch setup but I can't find the problem. How to fine tune the slipper clutch ? The instruction sheet does not give any clue.

Thank you for your help.