I think the difference might be the load on the engine. When you are putting it up at a 45 degree angle, you are simulating the load on the fuel and making sure it is still getting to the engine, but you can't simulate the unloading of the prop. Richening the high speed needle should give you a little room for when the prop unloads, but doesn't simulate the effects on ignition timing. I would recommend the same mixture of oil and fuel, but if you can try some fuel without nitro, I would be curious to see how it runs. My Aviastar was also recommended to run with 10% nitro, but it didn't work so well.
Good Luck,
Curtis