A couple of things. Yes a well lubed patch will probably not continue to smolder, but I have seen them do so. Plus there is a lot of fire coming out of the muzzle regardless if you used a conical or a patched round ball.
So..., you might stick with 3Fg if possible as it tends to burn faster and if it ever clumps it won't be nearly as big a clump as you'd get with 2Fg.
You might try putting a felt wad that was soaked in a borax solution then allowed to dry, between your powder and your patched ball. Would keep the flame away from the patch.
And as suggested just be alert to the direction you shoot in case you get a spark that lands. Also remember that when you are standing there is more distance for the ignited powder to travel before it hits the ground so more chance of a burnout, than if you're sitting/kneeling. In your conditions if you're firing prone..., you're going to ignite some brush. If standing use a tree to help steady your aim for a 50 yard shot or farther.
LD