Comb sort average complexity
The average-case lower bound for uniformly distributed data is $\Omega(\frac{n^2}{2^p})$, $p$ here denotes the number of increments, not actual gaps.

The number of passes is given as the input with gaps, which are in form of list, say $\{k_1, k_2,\dots,k_p\}$ where given $k$ is single increment value. There are $p$ increments to go, this $p$ is in the equation.

To avoid explicit list one may use shrink factor, which behaves similarly to shellsort and use the gap divided by consecutive powers of this factor.