not sure if i can fit bigger tyres due to the slick mudguards, but it might worth a tryChange your tyre size (the tyres on the bike). A 6-7% error is well within the speed difference commonly seen even in cars. They seem to be respecting EN15194 to the letter because power is supposed to diminish and cut out before or up to 25 km/h.
the controller is not programmable, this bike does not even have an LCDOn some bikes, the controller is made for several wheel sizes, therefore setting a smaller size than actually fitted, will give you a higher speed!
But you might be illegal, but at least you can "lie" and say it changed itself somehow!!
Its the cheapest method that I can think of!!
But as I said, in most countries (all EU at this time) illegal!!
Remember, you will regret this if you have a hefty accident!!
Regards
Andy