Stone shape ruling question

I have a player who is a genie warlock and wants to get creative with the spell stone shape. They are new to the game and excited to experiment. I want to give them clear expectations for how I am ruling the spell at the table.

By the text, the caster must touch a 5 by 5 by 5 foot cube of stone, and the new form they give it must remain within that same volume. My ruling is that the resulting shape cannot exceed the original amount of material. If the player wants to stretch a cube into a long slab that keeps the same volume, that part is fine, but the slab still needs to fit inside that same five foot cube. In other words, they cannot use it to extend stone far outside that footprint.

They also asked whether they can use the spell to drop the floor under enemies. I allowed that use, since the targets get a Dexterity save to move clear of the sudden change. They also wondered if they can pull stone from beneath the ground and bring it somewhere else, for example to create cover. My ruling is that they cannot relocate stone to a separate position. The material must stay within the touched cube.

They asked for clarification about the rules as written, so I want to confirm that my interpretation matches the intent of the spell and that it stays fair to both the player and the game.