UA's and LH's mileage calculations differ.
LH calculates miles from 'town' to 'town' (Example: Frankfurt to New York, crediting/charging the same miles to any of the three NYC airports: JFK, EWR, LGA).
UA 'calculates' point to point (individual airports).
This difference can work for or against me/you. I get more miles on LH's miles&more program flying the 'shorter' FRA-JFK distance. But when calculating for a rtw trip my mileage charge, I prefer UA's system 'charging' me less miles for that distance.