So let's just imagine this.
The Norks fire a Hwasong 12 on a high lofting trajectory (similar to their most recent tests) on a bearing SE towards Guam.
It's clear from that trajectory that it will land well short... lets say for arguments sake a good 100 km out from Guam rather than just the tens of kilometres short that Kim Jong-Un has been talking about.
Is that grounds enough to launch a few Bones and strike?
What if they drop one even further out - into the water halfway across the Philippine Sea on the same bearing?
Or just South East of Yakushima?
Pretty tricky tactical calculus in response; where's your red line?