This is the result of a typical shot (in 0 wind conditions) using the fixed power method of aiming. At the bottom you can see a copy of the cheatsheet I have taped under my monitor.
You can't see how I arrived at angle 67 just by glancing at this pic, but keep reading and you'll see it later. For now notice 2 things: The red power you see on the power meter is more or less exactly the power I use when I talk about "2.4 bars". I put the silver 'slider' right at the 2.4 bar mark, doing this makes it easier to drag or slice to the exact level of power you need. The other thing you should notice is that the distance for an angle 80 shot is also marked as the distance to make a good angle 75 SS at 1.9 bars.
Now you can see more clearly how I chose angle 67. I use right click while I'm waiting for my turn to come up and move the display around so that I am perfectly lined up with the left side of my screen/cheatsheet. Then I look to see what angle bigfoot is sitting on top of. Obviously if I'm shooting left, I mentally reverse everything.
In this case the enemy is between angle 65 and 70, but closer to 65, so I chose angle 67. Because bigfoot is below me, I know that 67 might land a bit past him. If I want a really good hit I must either shoot with a bit less power than usual or else try angle 68. I was afraid 68 would land too far in front of him, so I went with less power. It might sound like a guy would have to be nuts to be this precise, but it's not like that. I don't usually worry about how many pixels of power I put into a shot, just in this case I knew the hit had to be perfect to kill, so I really had to focus on getting just the right power level. I blew it by a few pixels but it's still a nice shot. Normally I just use the exact same power for all shots.