This might not be what you want to hear. But IMO, no accent tile will work best. It's a smallish bathroom, and that large glassblock window is off center. An accent tile would make it too busy for me.

If you are set on the accent strip, I would keep it in line with the window, just under it perhaps.

Thanks. I was actually thinking the accent might be too much as well. We're going to fill in the middle of the glass block window with glass blocks, which should look a little cleaner. Given the size of the window, do you think it'd be better to keep it "back" with the sill, or to try and make it flush with the tile?

Will you be removing that soffit? Doing so will also open up the space a lot. Are you completely opposed to either removing the glassblock and replacing with a window or sealing it up entirely?

The advantage you have in keeping it set back is using it as a shelf like you currently do. Bringing it flush with the tile will look a bit cleaner but you would likely have to add shelves.. again cluttering the space.

If it were my bathroom, and I were spending the $$ remodeling the entire thing, I'd really think about doing something different with that window.

Removing soffit is actually the first thing we're asking the contractor to tackle. Agreed, it should open up the space a bit.

We were leaning towards sticking with glass block because contractor said it would be less problematic (e.g. less drafty, etc.) So you'd put a regular window in? We're going to be adding a bathfan, so ventilation isn't an issue. And we can't imagine ourselves opening the window much.

Re: Sealing it up entirely: We really like the natural light. Would it be totally crazy to seal it up part of the way? (since it's so large).

I grew up with a 5x8 bath with this layout and window in the shower. It was a 'regular' window though, and I always really liked it. So I may have treated it like a sauna in the winter (opening up that window was great for the cold, fresh air).

I guess what I'm getting at is do you really like glass blocks? I think if it were me I would find a bigger window and then center it on the wall. Then search Houzz up and down for a bath I liked. There are tons of beautiful 5x8 baths on there.

Hi
We did a similar thing. The quickest way I can refer you to a picture is to try this old link from a remodel 4 years ago.

Here is a link that might be useful: glass block with accent