I guess the June exams cater for a significantly larger number of students so they are designed with difficulty in mind i.e. making the tests less hard to avoid criticism??? idk, ive seen that trend too, it doesnt seem very fair. Also, note that many do retakes so i guess they expect higher standards from them since they have had longer time to revise and to make up for that, they make the exams slightly harder so that the GCSE grade achieved is more universal