Do sub-10kt nukes really involve any fusion at all?
I have read of spiking conventional fission warheads with a core of fusible material to boost yield, but maximizing yield does not seem to be the goal of these devices.
One kind of the low yield weapons is to have very precisely placed smaller explosion - those ones is mostly fission core, and the other is to have high neutron flux with minimal blast effects - with that instead of a point you'd want to cover a wide area.