Distortion and computation error tradeoff
The computational complexity and efficiency of series representations depend on the number of terms used.
For map projection-based SRFs, distortion generally increases away from the origin.
Computational accuracy may be swamped by errors due to distortion.
Appropriate tradeoff of these effects are application dependent, and is central to determining validity bounds.
There is little published information to support a cogent decision on how to set the bounds.