Any way to keep this imp idle after firing?

Hey, I made a little map to show a conundrum I'm currently having. In Zdoom ports, you can shoot the pistol, hit the switch, and the monster will be facing the wall when he spawns, but in Boom ports if you fire the pistol, the monster immediately goes into attack mode when he warps in. Is there any way to keep the imp idle after firing?

Did you make sure he is deaf?

A thread where the question was asked and answered.

Setting a deaf flag won't change anything. As described there:

Foxpup said:

... What actually happens is, each sector has a flag that is set when a sound travels through it, and this flag is never cleared. Any monsters that enter these sectors will immediately wake up and target the player.

...

A wad that demonstrates ToD/Ribbiks's solution:

https://www.dropbox.com/s/pu6xm9o8k644ds3/imptest_crazyawesomedoburdwpacollab.wad?dl=1

I actually had to get rid of the soundblock lines around the imp for this to work, for whatever reason.

Aw shiiiiiiiiiiiiiiiiiiiiiit that barely helps me since my map is up to its neck is dummy sector garbage. Thanks a ton though rdwpa, I'm glad to at least have an answer to the problem; it's fortunate that Ribbiks literally had the same question, as my first instinct was to actually shoot him a PM in the hope for an answer :P

Alternative solution: Demotivate the player from firing his weapon in the sensitive area prematurely, for example by making him overwhelmed by teleporting Archviles or Cyberdemons if he does so (but not anymore if he fires after the intended monster, like the Imp in this case, teleports in).