Stealth

We seem to be of a similar mind of this, as I also do just about the same.

Usually I roll the distance of the encounter first, consider the terrain and move onto what will be the most interesting in the narrative.

For example,

Random Encounter, Western Ramps, Raiders x12, 250m.

Me:  You've just negotiated a bend in the road, the western ramps loom ahead a known and popular ambush point for the several snaking roads and towering concrete edifices of a long dead age.  The cart you've brought with you can't easily be disguised, the churning wheels banging off the uneven ground would have been spotted a kilometer away, if not heard.  You have the option to dismount now and disperse among the debris, making slow work forward, or sending a scout ahead to look for the presence of an ambush.

At this time the players usually select a scout or two, these players roll their stealth and move into the ambush site.  I don't roll the raiders stealth, I ask for a perception type C from the players to spot the raiders hidden in the ruins, laying in wait.  If their successful they can discern the raiders locations, along with any prepared traps before sneaking back to their allies and determining what to do from there.

I try to rely on the players skill rolls and checks and just assume the enemy has been able to move to their current location undiscovered for a time, but like with the Hell Cougar that gets up close, the initiative winner if the cougar gets all the benefits of hitting a target that is unaware they are about to be attacked.  You'll usually only have this happen in swamps or forests, and even then at night with the severely limited vision each provides.

(Accidentally hit post, sorry I am on mobile)

But my initial thought was to move the test four points from A (so a type E test) with some variance naturally on the situation but I wasn't totally sure.