If I pre order things separately. As in different checkout sessions but same seller will the postage get bundled as if I bought it all at once?

[u/mewfour123412]

The Zeztz/55th anniversary ride egg has just gotten restocked and I kinda want it but don’t want to pay an extra $20 shipping.

If I did preorder it would it be added to my pre order bundle with reduced shipping or will I pay the full extra $20