I think yesterday I figured out one of the reasons for resource sink (or maybe the main one). And, that is the lost build storages. After analyzing my 72h savegame, I got 123 of 261 total (i.e. 46%) xenon's build storages are lost (no station associated with them). But miners still deliver resources to them instead of wharf/shipyard!
This report gave me this idea. I have observed the behavior of xenon miners (quite strange) in their sectors. Now I made a bug workaround and want to check if my game will get better. Then maybe I'll add it to my mod.