Okay, but then make it impossible to place the flag in the “king of the hill” zone 
Also, a fixed radius has its pros and cons. The way I see it, the pros are: 1) you don’t have to bother with upkeep mechanics, and 2) it would lead to interesting base architecture. The major con is that there is no flexibility involved. An alternative is to combine the upkeep mechanics with the claim flag, something along the lines of the claim totem I once proposed.
It’s funny how the claim flag mechanic keeps popping up. It’s been proposed before and it keeps being proposed. I still keep a slim hope that Funcom is reading this stuff and that one day they might implement something like it.