I prefer to use target based stat, to determine the chance to see/hit.
Eg roll over target stealth value to see/hit it.
+1 to stealth value if;-
Target in cover ,
Target over 24" away,
(For every 12" over 24".)
Target using stealth equipment/ability.
+1 to dice roll if;-
Attacker has scout/recn equipment /ability.
Target less than 12" away.
This simple to see/hit mechanic takes target and attacker disposition into account.(Where as the fixed roll to hit just ignores everything but the attackers basic skill!)
(We can represent BS of units directly with thier effective range.As better shots can hit things further away!)
But score based on stat modified, and comparative stat based target scores , are my fovorite game mechanics.