Enemy spawn in Dark Sector

[MC Viking]

Anyone who knows with certainty what makes two big enemy ships spawn instead of one the second time you meet it in the level Dark Sector? I just can't figure out what the conditions are that make them spawn. It really does not make any sense. And my old faithful friend Google has failed me, I have not been able to find any website or forum with a certain answer to this conundrum.

I am trying to do Gauntlet on divine and quite often actually I get my ass kicked because they spawn. It's really annoying because first: lives lost, and second: it breaks my flow of the level and therefore makes a possibility of more lives lost.

That's one of the reasons it's my most hated level. So if anyone know please share your sweet knowledge.