My first instinct is to run it only on the long wall as it may be too much for the space. I would paint the other space and leave it without a back splash. To be safe, why not order enough for both? It looks like the other back splash space is maybe 3sqft? Unless your tile is super expensive, might be good to just order the extra and decide later.

I would definitely tile both spaces. I think otherwise, it's just going to look disjointed and you are going to have the dilemma about how to intergrate/blend/match paint or tile, etc. HeadACHE. Now, you get 2 opinions. Opposite. Which one resonates more with you?

Both for functionality if nothing else. If you've ever removed a roast from the oven or salmon from the broiler, you know there can be splatter.

Did you choose a really busy tile?

Williamsem
I like both runs tiled in your pictures. It gives a nice balance and also functionality.
Is that your tile?
Pretty!

I think both runs, but you know me with tile. The more the better....

You're getting close!

I would tile both runs. Much better balance that way.

I would tile both runs for balance and cohesion. Love the tile, BTW! What is it?

Another vote for tiling both runs.

Wow, didnt expect there to be so much agreement! That short side is 39 inches long with 30 inch deep counter.

Yes, that is my tile pictured. Though I couldn't make it any smaller, so the scale is off. That's a 12 inch sheet pictured, so it would be smaller IRL. I guess it is a little busy, but all the same so I think it will not be overwhelming.

It is MOP diamonds from builderelements.com, the only place I can find it. They are a bit restrictive, so if I order enough for both areas and decide not to tile the small area I can't return it. And if I want to order more, there is a 5 sf minimum. Not the end of the world, but at about $19/sf it's already a bit of a splurge. I seem to have good taste in tile, anything else I like seems to be at least 50% more so I just keep scrolling before I fall in love!

Go for it.
So exciting for you and can't wait to see it!
Our second backsplash run between ovens and fridge is 45 inches.
I use the counter and a boos cart for baking. My KA mixer has sent batter and flour flying - so glad I installed it.

Personally, I would tile both spaces. For me it would feel a little unfinished to skip the smaller space next to the ovens.

It'll be gorgeous - remember to order at least 10% more than your total square footage for cutting/errors etc...

I can't wait to see it all come together.