Tacx Neo calibration

Someone please explain how a 52x15 gear ratio at 100rpm equates to 18.5 mph?  After a severe illness, I was finally able to get on my new Neo trainer.  I attempted a power workout at 60% of FTP and became very aggravated.  I didn't notice it at first, but, when I had had to use the large chain ring, I wasn't producing the same speed as I do on the road (or the previous Fortius trainer).  A 52X15 gear ration at 100rpm produces +/- 28 mph.  The wattage was set at 186 (60% of 310 watts).  I have done similar workouts (at 60% of normal) on the Fortius trainer and the speeds were consistent with what I would see on the road.

To further aggravate me, a 52X17 gear ration at 95rpm resulted in 20mph (198 watts).  This doesn't make sense, am I missing something?