0 degrees.
Soft.
There isn't one because conditions determine the amount of it. Humid vs. dry, dirty vs. clean, waxed vs unwaxed.....
Some aiming systems, such as CTE which I use, seem to guide the user to a slight overcut which seems to deal with CIT nearly 100% of the time as far as I can tell.
(don't mention that you might consider trying an aiming system though to deal with CIT or it will start a shitstorm)
Not my intention to start or perpetuate a storm of any kind. Just an observation. As one who is trying to improve my play in a number of ways, I have found that working on positions and processes is very helpful in causing me to be in better alignment, sequence, etc., but it is my sense that superior play comes only with freedom from the rigidity that typically attends play based on a system (aiming or otherwise). Put another way, training with tools is a good way to train, but consciously using tools rather than the instinct that the tools have helped develop is not ideal. This passage from an article written by Darren Appleton helps put this (and the place of fun) into focus for me:
"There’s also many players these days buying too much into aiming systems.
"Don’t get me wrong, I’ve been sucked in too, and some systems are OK for certain shots (especially if you’re struggling) but 90% should be all feel and muscle memory. If your fundamentals are good you don’t need any aiming system.
"With solid fundamentals and a good eye for the ball, the rest will come naturally. Once you’ve played most shots thousands of times, you know where to aim. Aiming systems take the fun and skill out of the game in my opinion. Feel and vision are more important and more fun — all the best players play on feel and vision."