“Moreover - certain shapes of objects ( pillars ) do exhibit such behavior, whilst other ( broad walls ) simply explode, even though the same amount of force or damage is applied, and they have the exact same destruction thresholds set.”
you need multiple debris depth layers
and then you change what the minimum fracture depth is
if you dont want the entire thing to explode
what you are decribing as a “problem” was actually my own personal intended design, to have different results you need to look deeply into the apex settings
this is not as much an UE things as it is a Nvidia thing
you should go to their youtube on apex destructibles to learn how to only fracture parts of a mesh, and then you can use UE’s inhouse support for these features in the destructible editor
As far as how I achieved my results, I already posted the relevant code
you can just spawn an ADestructibleActor and you are good to go 
Rama