It doesn't state that because <caster level> = <caster level>. Why do we need to state that explicitly?
A 3rd level cleric with Brew Potion and an appropriate domain ability for the spell can set the caster level at 1, 2, 3, or 4. Of course that will cost you 25, 50, 75, or 100 gp to make.
You are looking for a loophole, maybe you should justify it?
Wands & scrolls of Hold Person don't care about what your Wis score is or whether you have Spell Focus: Enchantment either; the DC is set by the spell level. Why should a domain ability be different?