You DO have to play with these things to get them right.
On mine I used 15% of wheel base for my sidecar wheel lead.
I used a binder strap from the frame through the wheel to simulate me sitting o the bike - made adjustments easier.
Also, after you have adjusted the bike - roll it back and forth before you take another toe-in measurement, often the tires will bind on the floor and readings will be false.
Tire pressures DO effect the adjustments. I ran mine up, which makes the bike steer easier and the adjustments were easier as well.
I'd read all the blogs on set-up - etc..... It took me a few practice adjustments before it all made sense - then I really make some head way..... practice makes perfect.
Mine came out good enough that I do not feel I need leading links nor a dampner.