Okay, revealing a small bit of my power level: I have done professional editing for more than 10 years. While I have a different job now, I use my less busy periods to take on freelance editing jobs because I enjoy it. I usually edit to University of Chicago style, rather than Associated Press, because I'm normally working with books, not journalism.
Titty Master Ambrose is absolutely correct. That expression did not need to be hyphenated in that case. You would hyphenate two descriptors only when using them as a compound adjective, as in "We bought the less-towering Christmas tree because we have low ceilings." In that case, "less-towering" is an adverb and adjective joined together to form a single descriptor meaning "shorter." But if your character said to the tree salesman, "I want a tree that is less towering than this one," there would be no hyphen.
I've explained this before, and I'm sure, like the extra-tall (hyphenated!) Christmas tree your character didn't buy in my example, it is over TJ's head. I am just pointing out why Ambrose is totally correct in this case.