i fail to see the conspiracy here.
you trying to say these obstacles only spawn in these two places? Because you saw a few that had them just there?
my tree is in a different spot and my gemboxes spawn all over the place. But considering the millions of bases out there and seeing how full your example bases are already...there are bound to be some that have them in the same spot.
My my theory is they spawn in patterns and if you happen to have that spot free there you get one, if not you lose out in that round. Next spawn pattern is different and maybe you get lucky. I may be wrong but in any case it's random ...otherwise we would have had them spawn on our own bases in a dicernable pattern by now, no?