Can I fly in and out from same 3rd region using 72 hour visa free transit?

I have a Romanian passport and will be visiting HK and Macao. I am interested in flying from HK/Macao to either Beijing or Guilin to visit surrounding areas for 72 hours or less, and then flying back out to HK. Can I fly from and out to the same 3rd region and still use 72 hour free transit? (from HK to Guilin back to HK). Or do I need to fly in from a different 3rd region than the region that I am flying out to? (for example fly in from HK and fly out to Macao; or fly in from Macao and fly out to HK).
Thanks