Royale Ohoka

For this simulation in the transonic mach regime of a 2D Airfoil, what Bias Factor would be reasonable for me to use when creating my mesh? Some tutorials said 50000 for Reynolds numbers of a fe million whereas my analysis is approx. 15,000,000 Reynolds. 

Also, should I keep the selected 'Bias Type' or choose another option?

I am doing this in the hopes of cleaning up my aspect ratio and hence ortho quality.