Learn English – What does it mean to give somebody “a less than favorable review”

This kind of phrase is often used in tests and can trip even the most seasoned reader if only a casual assessment is made. In effect, this is a verbal representation of an equation.

"A is" allows for the basis of the resolution, "A = ".

"2 less than B" expresses a value of B, less 2, to assign to A, eg "B - 2".

Note here that the entire context of evaluation changes if something as simple as "than" is omitted, eg "2 less B", which would result in "2 - B".

The correct evaluation is "A = B - 2".

Less so is a “contextual comparative” and it modifies another adjective indicating a lesser degree of the quality in question.

In your context it refers to the adjective “quiet”.