Pop-up positioning is still off

[birtles]

I fixed one regression in 6f604ee where we would almost always put the popup below the text in desktop mode even when it would fit above but not below. However, it's still not right.

Here's a screenshot from Slack where the popup should be placed above since you can't scroll down.

[birtles]

I've applied a fix for this but it means that on sites like Slack we end up using the horizontal positioning more often.

Although this is working-as-intended, I'm not sure I like it. I wonder if users will find it distracting that the popup can now appear in any which what direction as opposed to simply above or below.