Reply from Easy Jet to the different sizes for cabin baggage...
Thank you for contacting us.
I am pleased to confirm that each passenger can carry one item of hand baggage, with no weight restriction, although you must be able to lift it into the overhead locker unassisted.
So that baggage can be stored safely in the overhead locker, the dimensions cannot exceed 56x45x25 cms (including wheels and pockets).
I think that this is a case of the right hand not knowing what the left hand is doing but we are back to the larger size so all's well...