Simple Random Encounter Rule for Dungeons

I use two rules for Dungeon Random Encounter. First one is as per the LBB:

Wandering Monsters: At the end of every turn the referee will roll a six-sided die to see if a "wandering monster" has been encountered. A roll of 6 indicates a wandering monster has appeared.

So every turn (two moves, 120 feet, which I interpret generally as two room or one room and one corridor), you roll for random encounter. On a 1/6, it happens. They see the monsters (not withstanding the surprise) as per:
Sighting Monsters: Players will see monsters at 20 - 80 feet (roll a pair of four-sided dice to determine the distance) unless they are surprised by the monster.

The other I use is the simplest version. I'm tempted to only use this one, as I am a huge fan of simplicity: every time the torch goes out, so every 6 turn, there is a wandering monster encounter. Of course this has two problem:

• You need to calculate for the lantern (a simple d6 that you turn on your side of the table is quite easy)
• Even if the probability of 6 turn on 1/6 is in practice almost the same, in theory it is not. You could go for 100 turn without an encounter, or 6 encounters in 6 turns when you roll a dice. Whereas with this method, you WILL get an encounter every 6 turns. 

You could switch it up to create tension, such as rolling on turn 5 of the torch, and having an encounter on turn 6 if you didn't get it on turn 5.