:x: 
<small>:x:</small>
<small> :x:</small>
Any other character, even a single space, will prevent the emoji from having the only-emoji class that makes it bigger.
I understand how it behaves like this and my guess is this is not very simple to fix, and it is also an edge case.
But I guess it’s always worth having a record of this minor “issue” somewhere, hence this topic.