A pedestal sink requires a minimum of 4" between the side edges and a wall or obstruction, so the distance may be based on that code requirement. I would want more, I think.

Good question, does anyone have an answer? How much space should I leave around a freestanding tub? Also, I see that some baths have beadboard around the freestanding tub. Is this a good idea? I seems cheaper and easier to install than tile. Do you just hope water doesn't spray on the walls?

I had a free standing tub next to the wall and a wall mounted faucet. I also had bead board around it - I am not doing that in my new house because it does get splashed. I had no trouble cleaning around the tub........ I just pushed the mop underneath.

You don't need the NKBA 21" minimum on All sides, only the side you are entering or exiting the tub from. On the other three sides I think you would want at least 4" between the outside edge of the rim and the wall so you could clean around it and easily retrieve anything that fell between the tub and wall. (Which is the purpose for the measurement for sinks that do not abut the wall directly).

I am planning a 66 inch freestanding tub centered on a 76" space giving me 5 inches on each end. I will plan 4 inch clearance on back wall under the window. Does this sound adequate? I do have room for clearance if needed by making my shower smaller. What did you end up doing for yours?