Well, I think I found the cause of the issue. We are using a wip engine version, which was provided to us by Stonetrip with a specific engine fix.
I tried now to create an apk with the old stable engine and with the new 2.0 exporter, and both apks have correct radius. So I'll need to contact Stonetrip about this issue after all. Sorry to cause you people some unnecessary rounds.
Thanks!
Makkar