Going back to the IP: Davis and Ackermann steering have nothing to do with where the rack is located. "Davis steering" uses sliding connections between the links while "Ackermann steering" uses the vastly more common rotating joints and fixed-length links.
Crispy's post makes a lot of sense. I'll take a plot of outside wheel steer angle divided by inside wheel steer angle vs. steering wheel angle anyday. That's what matters, right? The simple geometric approximations and associated terms ("percent Ackermann") can give a reasonable starting point and a general idea of the behvaior, but cannot describe the full range of operation due to their assumptions.