Why?  because of the difference of actual weight and Volume weight?  for example:

Sabre kit:  Actual weight is 3.0kg but Volume weight is 13kg 

Penguin Kits: Actual weight is 3.5kg but Volume weight is 16kg

EMS Will choose Actual weight

DHL/UPS/Fedx: will chose Volume weight

So DHL/UPS pricing will be double or Triple. So if order Airplane kits (ARF) please choose EMS.  

DHL/UPS pricing of our shipping system was Actual weight only, not Volume weight. it's invalid if order Airplane kits (ARF) only