In single-player or on private PVE servers, it is common to have multiple bases all over the map. One of the reasons that the purge gets disabled is because it is impossible to defend multiple bases all over the map.
Suggestion #1: Could you please provide an optional setting to force the purge to target a player when they are near their base? The player/clan will still head for their base when the purge starts or be forced to fight at a disadvantage, because defending is easier than attacking in an open area.
Possible Caveat: Players standing in bases that are unreachable should NOT be targeted to avoid the purge from originating inside the base. If you have to climb to your base or use an elevator, you are already disadvantaged.
Suggestion #2: Could you please have the purge originate from an NPC base (dungeon, camp, etc.)? That would add some exceptional realism and difficulty to the game. Defending bases near NPC camps would require much more effort.
Please review and respond with criticism (what could go wrong?) and help to elaborate on this idea.