We recently acquired a Reach RS + antenna to measure GCPs for drone mapping projects. We are testing this solution with a national NTRIP provider (Orpheon / France) to achieve centimeter accuracy.
This week, to verify the good functioning, I measured known points that we had collected 6 months earlier for an old modeling project (using a Leica antenna connected to the same NTRIP network).
The precision obtained in XY is centimeter, there is a difference in average measurements less than one centimeter.
However, the elevation data show a difference of about 47m.
Like many drone users you are confused between ellipsoid and geoid.
You have substract geoid from IGN69 model. Your height is ellipsoidal whereas Leica applied a geoid.
In this part of France, you have to substract 47.7186. So elevation become GCP1 = 141,258542009, GCP2 = 140,879833953