Bathtub/Shower Valve distance to Tub Spout

Hi,

I recently bought a new Delta Intuition bathtub and shower valve package complete with the tub spout and shower head. The installation instructions say that the distance from the bottom of the valve body to the tub spout should be 8 to 18 inches. I am using this new setup to replace an older Delta valve body installation where the tub spout is slightly less (about 5 inches) below the valve body.

I was just curious why they would spec out the distance other than just for the convenience of having
the tub spout and valve body in "comfortable" positions. The tub spout seems at the correct height above the tub, and the valve is easy to reach as it is whether taking a shower or bathing.
Thanks

They err on the conservative side so the spout and valve trim plate do not interfere with each other.

The same valve supports many different trims...so, as mentioned, to ensure any one will fit, they define a minimum separation.

Thank you gentlemen