player XP in Heist, stand and fight or escape ASAP?

Hello,
Just wondering if you get a fixed amount of XP once the alarms go off and you escape in Heist, or does your xp completely depend on how many guards you kill (like in most of POE).
In other words, can I "farm" xp by standing and killing endless guards for 5 minutes, or is it a waste of time?

Thanks!

The first couple of spawns from each room give good xp. After that it's worth nothing.

Thanks for the confirmation. I thought it was something like the necromancers and skeletons (in their case, only getting full xp on the first kill)

Thanks!