Hi Alessandro:
I have a made a conscious attempt to correct to hip extension in planche as well. I believe I was having the same form as in push up for this exercise. Here is my attempt after that correction. It appeared to be a bit more easier to me than earlier.
Set 2 of 4
Here is the last set which is still a bit of struggle and I can feel my hands shaking.
I will glad to get a feedback on these.
Thanks
Krishnan