In an England shirt he is being asked to play a completely different role. More the creator than the executioner who provides the final cross.
I banged on about it earlier but City, Spurs, Utd who have a disproportionate number of players in the side play a variation of 4-2-3-1 yet Southgate decides to go with a 3-5-2. It is completely nonsensical.
I honestly do not think it is rocket science.
Rashford plays left for United play him left for England.
Sterling right for City, play him on the right. Same for Walker etc etc.
International football where time is limited, players have not built relationships is not the time for installing new systems.