A good tactic is to mine or wire the approaches to the pillbox/bunker, but leave its escape route to the rear clear, so the occupants can bail out when necessary and head via a trench or a tunnel to the rear where they can re-form, the now surrendered Pillbox will not do much for the enemy, its firing CA is facing the wrong way to be of much use on you. Those mines in front (or wire in front) will slow the enemy assault on the pillbox/bunker so you can get away when the enemy decides to go for broke.
Like any position on any ASL game map - never be too fond of it that you lose the units inside for no gain. If you have to ask yourself if it is now time to leave the position, you waited too long. "Stand and Die" defensive positions are for the last turn of the scenario - not the first.
Even a single board width scenario has limited capability for a fallback and/or skulk - both should be used to full advantage. Only hold onto the pillbox/bunker for dear life if losing it means you lose the game, too. (ie its occupation is in the VCs).
Another useful idea to consider if you have three pillboxes/bunkers is to look at the idea of the "death triangle" as a possible setup - where 2 CA's cover the NCA side to each of the other pillboxes/bunkers. Anything trying to get around to the NCA side of one is going to eat fire from the other two. It gets nastier if tunnels interconnect them, and even moreso if the last (third) tunnel feeds into say, a stone building nearby, so reserves can be fed into the death triangle. It is not suitable for every scen with pillboxes/bunkers, but should not be overlooked if you get three or more of them as a possibility.
no matter what, screen the NCA tops of the pillboxes/bunkers with MG fire - this can be a useful place to boresight a MMG or a HMG if allowed- you know the enemy is going to try to silence the pillbox, so you know your -2 Bore Sight DRM is going to come into play at some point.
KRL, Jon H