Ultimaker's displayed print-size is wrong/misleading?

[LordVictor 0]

So I'm trying to print something on an Ultimaker 3 extended, which should be within the specified size, but it has to be reduced to 80% or smaller for Cura to slice it, making it completely useless to me... Does anyone know how to solve this? Otherwise I should think Ultimaker would need to correct those dimensions on their site, as they are seemingly very 'misleading', to put it as nicely as I can. You can see the print below - it is within the limits, with a bit to spare, but needs to be drastically scaled down for it to slice. 

[IRobertI 516]

https://ultimaker.com/en/resources/44677-maximum-build-volume-ultimaker-2-plus-ultimaker-3