I've tried distances ranging from 30nm to 60nm, unless there is a specified VOR changeover point on the airway.  I manage radial tracking very well with heading select mode, it would just be nice if I could get the autopilot to do it without wandering back and forth.  The strange thing is that when I manually align the radial and have the CDI centered, if I switch off HDG select and let VOR/LOC mode take over, the autopilot immediately deviates off the course.  It then starts wandering again to the left and right, obviously not keeping the CDI centered. :-?