A pro trike builder advised me to reduce the caster angle. What I did is place new braces for the bottom rod-end bearing with a sort of bulge. He is probably right. Steering feels nice and light now and the rear wheel is not leaning as it used to do.
Of course there are other ways to modify your trike for a reduced caster angle then the braces I made. Keep in mind the bottom bracket has to be at 30cm for heel clearance. On a higher trike the main tube can be horizontal. But the lower the trike will be, the more angle you need to reach the acquired BB height. Therefor the correction of the caster angle must be done in the kingpins itself.
I will add some more pictures later.
Notice the approx 12 degree caster in the previous design isn't that bad for handling. But a bit less angle will improve overall performance. That is the idea.