Like previously mentioned, AFR is just a number that depends on a lot of factors. Tuning a 2 stroke is not the same as a 4 stroke. 2 stokes are more sensitive to heat and thermal management. Therefore, a best practice is to enrich the fueling until the sled starts to misfire and sputter at WOT. At this setting, the sled should color the snow with the unburnt fuel in the exhaust. From there, start to lean it little by little until the combustion cleans up...you may still be painting the snow with fuel at this point. Then, I personally like to go a little further until the sled stops painting the snow with exhaust. At that point, I stop. You can tune fuel up or down a little depending on power, which you will feel the sled getting stronger as combustion optimizes. However, stay on the rich side to keep the pistons cool while climbing. Finally, the larger the piston bore size or increasing boost, the richer you should run it.
I run a 600 cc turbo at 12.8 to 13.0 on the gauge, not because the number, but because that is what the sled wants. It has been happy for may years at 12 psi. Comparatively, most 4 stroke engines achieve MBT (maximum best torque) at 12.8. My 400 hp capable viper is setup to run 10.8 to 11.0 at 30+ psi to cool the pistons. From 12 to 16 psi, that same sled runs 12.3 to 12.5 all day because that is where it is happy without going to lean. It makes more power at 12.8, but the lower number keeps the engine cooler without sacrificing much power.
In short, tune the sled to what it wants, not a number. It will tell you what it needs, from there stay on the side of extra fuel without sacrificing throttle response or crispness. Also, the sled will be lean on light throttle, 15 to 17 is not uncommon. But, keep in mind, lean is not bad in that situation because there is relatively no load on the motor to create heat. Lean is not what melts pistons, it is heat generated under load without sufficient fuel to cool the pistons.