You probably need to use a search area effect or a damage effect, setting it's effects to do area damage, with target impact location set to target point, as the impact effect of the launch missile effect of the battlecruiser weapon. If the effect set as the impact effect of launch missile effect of the attack of the BC, is a regular damage effect with the "Target: Impact Location" set to target unit, when the missile arrives at its final destination and executes it's impact effect, it will damage the unit targeted by the attack, wheter or not is within the range of the impact of the missile.
You may also want to check this video of how to make an skillshot ability, since it accomplishes something similar to what you want to do. Link below.
You should read the sc2 mapster wikia entry on the parameters of the launch missile effect, to give you an idea of how to accomplish it, link below.
https://sc2mapster.fandom.com/wiki/Data/Effects/Launch_Missile#:~:text=the missile impacts-,Effect - Launch Effect,of the Launch Missile effect.
You probably need to use a search area effect or a damage effect, setting it's effects to do area damage, with target impact location set to target point, as the impact effect of the launch missile effect of the battlecruiser weapon. If the effect set as the impact effect of launch missile effect of the attack of the BC, is a regular damage effect with the "Target: Impact Location" set to target unit, when the missile arrives at its final destination and executes it's impact effect, it will damage the unit targeted by the attack, wheter or not is within the range of the impact of the missile.
You may also want to check this video of how to make an skillshot ability, since it accomplishes something similar to what you want to do. Link below.
https://www.youtube.com/watch?v=xradjsdTlfg&ab_channel=LazZ'sMapmaking