I think experimentation is needed with dose size and release rate. For me quick-release is ineffective, while 750 mcg slow release is great. But some do get next-day grogginess from higher and more extended doses. Paradoxically I find that higher doses impair sleep.
Recently I used two tablets of 2mg Circadin (Melatonin ER). It did sweet jack.
Perhaps the dose was too high. The tablet can’t be cut I presume without losing the ER.