Hi Bas,
May i know what is the XMC version?
starting from 7.x the image scaling size is increased and there is an option to customize the same.
This can be done by editing the NSJBoss.properties file, the line which needs to be edited is oneView.maxImageSize=3000x2000 (this value is by default) , can you check the actual scaling of the floorplan image and set the oneView.maxImageSize accordingly and see if that helps?
please note a server restart is required for the changes to take effect.