Yamatai’s torpedo doesn’t have a range for its explosion of 3 light seconds. And this warhead is literally like stuffing a destroyer sized shock cannon in a missile.
You are trying to put a weapon completely equivalent to the main gun of a plumeria inside a missile.
There’s a reason that this is OP: it’s a tier 13 weapon which effects a 899377 km long cone.
As a main ship weapon, which you based this warhead off of, those stats are fine.
For a 2.4 meter long missile, not so much.