That’s what I thought as well. But things are just not working correctly.
If I use the URL with just an &, it re-encodes it using & # 0 3 8 ; (no spaces).
If I use & a m p ;, it keeps it as & a m p ;
I’ve tried other combinations as well but it will never simply encode using the & (e.g. &eml=xyz.com&cid=abc).