Low quality on ar.js with portrait aspect ratios

So I’m having some strange issue. I’m using ar.js with Three.js, and it seems like when I use different aspect ratios the quality drops significantly (like on a phone’s protrait mode). I added two pics for comparison.
If using just plain Three.js (without ar) then the model looks sharp in all aspect ratios. Any idea why ar.js could cause this, and how can I fix it?

Some hint that I found:
If I remove the line
Then the model just appears squished (on the x axis) and sharp.
I think it renders it thin and then stretches it to the original width, which makes the quality drop.

Let’s see your code! What code is being executed when the viewport size changes?

I pretty much use the same code from the samples:

    function onResize()

        if ( arToolkitContext.arController !== null )