Yes, there are a bunch of rules of thumb with this stuff. Thickness (in part due to localized deformation; which would make the Single Degree of Freedom Model worthless), width (which helps with the rocking motion), etc, etc.
But I've seen these "rules of thumb" get people into a lot of trouble. You have to really be careful with this stuff.
Another one I see people do all the time is: they treat the calculated spring constant like it's 100% accurate. It isn't. The actual value will fall within a range of possible values. (Depending on the geotechnical work done.)