Yep.
You pay postage on anything you put into your POL. It is based on what it would cost should you ship it right away.
If you add something to your POL and there is already something in there, they calculate the total cost of shipping everything together and you pay the difference when you pay for the new items.
So for example, lets say postage for 1 deluxe is $10, postage for 2 is $15, and postage for 3 is $17.50
If you buy one deluxe and start a pile of loot, they charge you $10 for postage.
Then later you buy a second deluxe and add that to that pile, they would only charge you $5 postage for the second figure.
If you later buy a 3rd deluxe and still have that pile sitting there, they would only charge your $2.50 for postage.
Rinse and repeat until you ask for them to ship it to you. They then don't have to charge you anything when you ask them to ship it. Means less transactions, it's faster when you ask for it to ship it, and you don't have to worry about how much the shipping will cost as you've already payed it.
If your pile builds up enough it can get to the point where you add an extra figure and it doesn't charge you any extra shipping.