In my experience, aquaplaning due water depth is not the problem, oil and rubber are the key. If there is a little rain, after a long hot summer, the oily surface can become like an ice-rink.
Though water depths over 1/2" can definitely be problematic, I fully agree with your observation regarding oil and rubber deposits on the runway mixed with a little water.
Been there. Done that. Had the ever luv'n ****e scared out of me.