To my eye, often times the dimensions work in step with the size and detail of finish materials used.

The dimensions can also be affected by the tub being a drop in or an under mount installation. For a drop-in, the height/width of the tub's rim could affect the look and how you'd want to detail it.

As to the width of the front edge of the deck, how high is the tub deck off the floor? Meaning, is the tub low enough where you simply step over the edge and into the tub? In that case a narrower edge might be more practical. Is the deck high enough, or would the bather prefer to sit on the deck's edge and swing him/herself into the tub? In that case you might want a wider deck.

All things being equal and without knowing the answers to any of the questions I've asked, yes, the edge would look in scale anywhere between the 5" and 12" of the deck's other dimensions. 8" to 10" might be a good compromise.

Mongo

Mongo, Thank you for your thoughtful questions. The tub is the Kohler steeping tub K-790 and it is 60" x 36" x 20-3/8"H and the placement is in a 3 wall alcove. The tub rim is fairly flat. We thought this height would be okay for stepping over while we're still spry enough and good for the sit and swivel method as we age in place. The other consideration I forgot to ask about is finding room for the faucet, controls and handspray. I wanted to line them up on the long step in side toward the foot end of the tub. Is a 5" deck too narrow to accommodate all of these items?

Unfortunately our first choice of tile was too much for the budget but we are hoping to find a 3 x 6 tile for the walls and to use a coordinating 12 x 12 for the deck surface.

Thanks again for your help.

The 790 works in your favor, for if I recall the height of the rim is quite small, less than 1". Maybe 3/4" or so.

Realize that in terms of the physical construction of the deck and apron front, if you have 5" or visible deck, consider how much, if any, overhang there will be in terms of the deck protruding past the front apron. Combining that overhang with the thickness of the front apron wall and that may be a consideration for plumbing clearance below the deck.

Most tiled deck/aprons have a square 90-degree turn at the junction with no overhang, that'll help you in terms of space plumbing space beneath if that's your intended design.

So as to the plumbing fixtures fitting on a 5" deck...they could easily fit, with some looking better than others. How well they fit and how good they look would depend on the size/style of fixture.

Mongo

After much back and forth with the GC and all other concerned I now understand why some of the "fancy" magazines show tubs with recessed alcoves at the ends or in the long wall opposite the step in side or show ledges or shelves in the same locations. Quite simply it's a matter of a tub being fitted to the space available and various tricks being used to make it visually appropriate. Quite a stretch for me but here's the final agreement by all.

The tub must stay where it is currently 12" away from the far wall opposite the step in side because otherwise it will seem to be recessed into a cave. The far wall opposite the step in side will have a 6" deck and then a step up of 6" to an 6" long shelf that will extend the entire length of the alcove. The foot end with the controls and the long step in edge will also have a 6" deck. The head end deck will be 4" wide. Although the tub will actually not be centered as to the head and the foot ends in this arrangement everyone assures me that it will look centered because the controls will visually fill the off center space.

We are weekss away from installation and tile work but I'll post pictures of how it all eventually turns out. I just wanted to thank all of you for your input. For now I'm taking a leap of faith and I'm envying everyone who has the vision to "see" the final product before the first nail is pounded.