All Epson's have a base adjustment for media feed. newer units have there’s set to 980mm as base line and using Epson double weight matte to set up. As I say, I doubt it’s the Epson at fault.
could be creepage due to inking, texture of media, environment etc. what you could try is using the remote panel software to open up paper feed in-between head passes to make up the short fall, however you may start to see banding.
