I am trying to change the sink in this bathroom. tha vanity is about 60 inches wide and is 22 inches deep. While it is not obvious from the picture, when you are standing in the bathroom, the sink seems tiny. The current sink is a Kohler Verticyl 17 inch model K-8189. My builder is telling me that the constraint is that the size of the cutout for the sink can not be more than 12 inches deep because 6 inches are needed at the back for the backsplash and the tap and 4 inches are needed at the front to ensure there is structural integrity of the vanity.

How much is really needed at the front for structural integrity of the vanity or is my builder feeding me a line hoping I'll drop the request to change the sink? If they are saying 4" is needed (and I'd imagine that something is needed), would only 3.5" be too little.

Assuming something close to 4" is needed, but there is some wiggle room I've found a vessel sink. Kohler K-21060 which calls for a cutout that mostly is less than 12", but is 12-19/32" right at the middle near the faucet OR the Kohler or K-21059-1 which calls for a larger cutout of 15-15/32" but because that sink incorporates the faucet into its structure, it would take more space towards the back, still leaving something close around 3.5" at the front and the back.

Any thoughts/advice that might help me better address this with my builder.