I have something similar, and since every touchscreen is slightly different i decided to run the calibration sketch and store the obtained values in EEPROM for the other sketch to use. Works like a charm only requires that you store the values in a location in EEPROM that is known to both.
Somehow there was some conflict on using the first 20 EEPROM addresses which may have been a conflict with the library i used (mcuFriend)