Concerning the meaning of "of" in "less of"

Question

Which specific meaning does the preposition of takes on within:

It was less of a thought than I expected.

?

---

Edit: the original phrase (before the first answer) was:

It was less of a thought than a feeling.

Answer 1

To my ear, that is ungrammatical, a mistake for "it was less a thought than a feeling".

Probably a blend with the different structure "It was less of a thought than I expected".