True, but will modulus prime be better than any other modulus at distributing the items amongst slots.
That is the general theory.
I have been looking into this a little, and that theory seems to be dependent on:
a. Whether the hashing algorithm is one based on powers of a prime (often 31) in which case you don't want your modulus to be a multiple of that prime; and
b. Hash tables which use strides when a slot is already used (rather than linked-lists for each slot as mIRC does).
Neither of these seem to apply in this discussion.