The default purchase distance for RUC auto-purchase is set at 1000km. This can be changed through the following steps:
Open up RUC Manager, under the Vehicles tab
Select the vehicle you are wanting to change the default purchase distance for
Select 'Edit' under the Vehicle Defaults box
Using the drop down next to 'Default Purchase Distance', select the new purchase amount
RUC Manager is permission specific, please contact your admin user or Coretex Support if you do not have access to this.