I need help with AdSense responsive forma

I am using adsense responsive format which is great for mobile users as almost 80% of my users are coming from twitter via mobile device.

But I have one problem that somehow I can't solve it.
When opening an article via PC the responsive ad is with a 468x60 format and I don't like it at all.

I would like the format to be 336x 280.
The only way I can do this ( I thing its the only way ) is to add a html box inside the article(wordpress) that has this dimensions and the ad will fill.

The problem is I don't know how to do this, if anyone can help me with this or guide me to an article to my solution.

I figure it out.

If anyone is facing this similar problem this is the solution
You just need to change one thing in the code

data-ad-format="auto"

you need to change the auto to rectangle

data-ad-format="rectangle"></ins>

Now the ads will only show in rectangle form but its still auto adjustable for the mobile users.