There can be differences between a RAMP test and your Xert fitness signature as Xert calculates the numbers based upon watts achieved while fatigued and the relationship between PP, HIE and TP.
For best results try a multi-dimensional test by searching the workout library for “breakthrough” and perform one of the BT workouts in slope mode on your trainer.
When you hit the section where MPA is purposely drawn down and you are about to tap out, spin up out of the saddle and try to sprint as hard and long as you can. 5-7 seconds minimum or longer is possible.
If you are new to Xert there are lots of tips in this thread –
Beginner questions - Support - Xert Community Forum (xertonline.com)
You can also ask Xert support to take a look at your data and adjust signature if required (support@xertonline.com).