My suggestion for making it a challenge was to let the sniper get one shot off at the start of combat if the party earned 8 VP in 2 rounds. If it is a boss creature, it’s DCs for perception are going to be high and even flat-footed the AC and HP will be high enough that one shotting the boss would require exceptional luck. I am ok with having that possibility.
Sorry, SB. While you technically can attempt to Avoid Notice with no cover or concealment, it means f-all because if you're out in the open you're immediately observed by anyone with line-of-sight. So cover and concealment is important, and is incorporated into the Stealth check "both to determine your initiative and to see if the enemies notice you (based on their Perception DCs, as normal for Sneak, regardless of their initiative check results)." ~ CR 479 under Avoid Notice, emphasis mineAvoid Notice explicitly uses Sneak rules, at least when initiative is rolled. And you can't actually Sneak if there's nothing to hide behind.No. Avoid Notice and Sneak are two distinct actions with their distinct rules. The bonus from Cover is only RAW for Sneak. Also, you can Avoid Notice even if there's no Cover nor Concealment.
If the Rogue opens the door while avoiding notice, they can use Stealth for Initiative even if there's an enemy behind the door and there's no cover nor concealment available once the door is opened. Avoiding Notice is not Sneak, you don't need cover nor concealment to Avoid Notice, which doesn't mean that you have to make silly rulings. If the Rogue is speaking with the enemy when the combat breaks they obviously can't use Avoid Notice, but if the PCs encounter a bunch of enemies at a corner, you'll allow Avoid Notice without checking for Cover or Concealment because when combat breaks the Rogue was technically silent and stealthy.
On the other hand, you have to use Cover and Concealment to determine if the Rogue is noticed by the enemies, which is the point of the rule you quoted (the parentheses apply to "see if the enemies notice you").