Hi Jimbo,
Good question. There isn’t a way to do that out of the box, but contributions are welcome!
The reason for the difference is probably that Ephemeris uses position, velocity, and acceleration to interpolate while EphemerisSegmentPropagator uses only the data in the file to interpolate.
Perhaps the easiest way would be to implement your own EphemerisSegment that contains the data from several files. You would have to make sure they have the same type data available, e.g. if one file has only P records while the other file has V records as well that could create a mismatch.
Regards,
Evan