OK. For fireside gathering to earn just the card back needed to be at least 3 ppl on same lan connection and play 1 match eachother without even concide. Now that is Tavern brawl gathering is just to be on same location ?! Isn't it strange a bit ?!
On my tablet and phone searching gathering via connetction not gps. So, as I suspected won't work. I did it with fake gps and no nearby players or gatherings... Always it shows the name of my lan connection and not the location on HS