Old vs New [Tehenhauin] model query

[Zenai]

OK, I have acquired myself a old Tehenhauin model (which also had an Oxyotl model in the same blitz pack). Now, unlike the newer Tehenhauin model (which comes with a 40mm base), the old Tehenhauin model comes with a 20mm base. Now, am I suppose to put the old Tehenhauin model on the 40mm base or am I allowed to keep it on the 20mm base?

[Arguleon Veq]

He should be on the base size of the current model.