And actually, we KNOW the Red Miles as an attack don't typical have infinite range... We see it activated 4 other times by other weaker characters and those barely are able to spread across a planet like Derse/The Battlefield or the LOWAS (not even gonna get into the sizes of Homestuck's celestial bodies, those are somewhat inconsistent lol). It's only when amped by the fourth, most potent prototyping that Bec Noir has the power to create a version of the Red Miles that is able to destroy an entire Genesis Frog!

That and Jackspers (3x Prototyped Jack) wasn't able to kill Bro or Davesprite (even WITH the use of the Red Miles, on the LOWAS) until he gained that 4th prototyping! It's just super consistent...