Hey Gemini, i see you read the posts carefully
Offside trap is defensive tactics, it should be totally fine to use with defensive mentality.
I just leave it on most of the time with 4-5-1 unless opponent has really fast attacking line, offside trap would work better if it was zonal marking indeed.
in the previouse post i was talking abou 4-3-3 Attacking mentality formation, it's a bit different when it comes to Defending tactics as i would use Offside ON with any kind of defensive formation.
-It makes little to no difference tho.. as i've seen offside for opponent team even when my offside trap is off. it's just a little booster in defensive tactics.