Would the Magnificent Mansion if cast on a moving object remain where it was cast or stay with the object?


The question has arisen in my mind on whether when a mage has cast a Magnificent Mansion (5e) while on an object that is in motion (boat, airship, giant alpaca, etc), would the doorway to the Mansion then remain static in place?

The relavent wording from the spell: "You conjure an extradimensional dwelling in range that lasts for the duration. You choose where the entrance is located. The entrance is 5 feet wide and 10 feet tall…"

I could see that this would indicate that the mage has chosen the location to be the giant alpaca and as such that is where the door would remain located. Or that the mage has chosen the place in space that the door is located and as such the door would remain there despite the alpaca continuing to move forward. Or perhaps something else might occur…?