Tempest Trial rank reward

I just ranked ~12k in the Less Than Heroic TT. The posted reward from ranking between 10k-50k was 2k feather. But I received 4k feather from rank when I logged in this morning. Why is that? How exactly does the rank reward in TT work?

(It displayed 4k reward in the prompt and I am also certain that my feather count went up 4k instead of 2k.)