Depends on where the shower head is located. If it's on the same wall as the vanity, you will need glass. If you use the new taller height for the vanity (36") then a 42" glass topped wall next to that would be what you would need.

My set up will be something like this one, except I don't want the glass panel. And there will also be a handheld shower in the same wall as the fixed shower head. The width of the pony wall will be 40". Why would the height of vanity makes a difference?

Without glass, you will get overspray and water damage on the vanity. The glass partition is a functional portion of the design that cannot be eliminated unless you want to replace it with a solid wall there. The height of the vanity makes a difference as to how short the wall can be with glass, if you want that open look.

Look at the photo above, they even have the showerhead angled away from the glass partition ... it seem they are trying to reduce the amount of water that gets on the glass!

Without that glass partition there will be water on the vanity.

I have a glass partition as the side wall in our shower and the water spray goes up at least 4-5 feet.

How wide is the wall with the shower head?

The wall where the shower faucets go is 44" wide. The pony wall is 42" wide, with height TBD. The whole shower is 70" deep.

I don't think I have a photo from the same angle as your shower, but this may help. This is our master shower.

The wall with the shower head and handle held shower bar is 44" wide. (That is the wall opposite the controls.) The pony wall is 27" wide and 59" tall. The pony wall plus glass door is 55" long. That means our shower is about the same width, but yours will be longer.

This is our basement shower.

The wall with the shower head and handle held shower bar is 33" wide. The pony wall is 35" wide and 51" tall. The shower is 64" long. I don't use that shower. It is doorless and I have asked our guests if the water sprays out of the opening and have been told very little sprays out. I haven't asked about water getting on the plexiglass we have over the pony wall.

Our shower has a glass door and based on the basement shower not spraying the floor, you would not think the entire width of the glass door would get wet. However, it gets wet when I shower and I use the handheld shower head, but stationary on the bar. My husband uses the rain shower head and he does not get splashes on the door, but he gets a tiny bit of splashing on the pony wall glass. I get no splashing on the pony wall glass. Your mileage may vary.

Thank you all for sharing your comments and dekeoboe for taking time to upload the pictures for me. So looks like I do need a glass panel. What about maintenance? Do you find it hard to keep clean? I am more concerned about the nooks and crannies where the glass meets the wall/granite, and the area around the metal clips.