I knew you had the answer
.
For those who are interested: you have to copy the population of course, set the rotation of the copied one to 180° over X and don't forget to check "Sit on object" again under the Anchor tab. This isn't automatically copied with the population.
Thanks, Ulco!!
I hope you don't mind hijacking this thread, Archonforest, but your problem has been already solved I guess?