Not sure if this is your problem but here it goes:
Try rotating the Alpine fractal with the transform shader like 90, 90, 90 (or whatever works) for example.
It could be that Terragen works more from point zero that is on the north pole basically.
Some displacement looks stretched on the equator (what looks normal displacement on the pole can look like stretched lines so far lower you get).
Basically Y stretching,displacement most probably.
As much you can do planetary things in Terragen the safest way is to play near the place where the default camera is.
You could go just higher there, use a similar setup and look down that will seem like the equator anyway.