I believe that the toe in/out depends upon whether the craft is a tricycle or tail wheel. In a tail wheel the C of g is Infront of the wheels, this is critically stable and can lead to instability very easily. I understand that on a tail dragger toe out is better as it acts quicker and pulls the craft back to a more straight line during landing. Landing is where stability is critical, taxying can be less important and whilst annoying I think that most manufacturers look to landing characteristics. Tricycle craft have the C of g in front of the wheels, somewhat more stable arrangement for landing. It is my understanding that manufacturers will arrange toe in/out on tricycle craft so that from touchdown to relatively slow motion that the wheels are close to zero toe in/out. The toe in/out at this point of relatively low loading depends on the way the undercarriage moves with camber and caster and forward alignment during the process of undercarriage loading. I think that as you can only adjust the undercarriage alignment during stationary but light to medium loading is critical then it is trial and error, unless you have a finite element program and lots of time to calculate a variety of options, and of course springs vary so much that you would have to test the spring rate.
I have no idea what your friends problem is caused by, I suspect spring geometry or an undercarriage wear problem or change from original, but if one craft behaves differently to another of the same make and model I would carefully examine the whole system including location to the frame of the craft.