So I found I struggle with cutting a ball frozen on rail to my left if using low left( assume I have to for position). Anyways I know if I were to use running English I would have to hit ball and rail at same time and aim to hit a hair fuller to compensate for deflection. Anyways what was surprising is I am only able to consistently execute the low left shot if I aim the same way as I do for the running English. In theory I should have to compensate for cb deflecting to the right but somehow works when I compensate the opposite way. Weird!
In a video Tor Lowry demonstrates that the position for that shot is very close to straight low. The left does complicate the shot because of squirt and the reaction with the rail if you hit slightly rail first. The outside spin does widen the angle a little and there may be times when that is critical but you might experiment with and without it to see how close you can come without it.
In my generation most of what we all learned about pool was trial and error and from friends. Now days there are all the training videos to disprove so many long held beliefs. I don't think I ever hit a draw rail shot without side spin for years.
All that said, I have shot that shot for years and simply developed a feel for it. I actually am more accurate with it then without the left. I can't say for sure but I think I hit slightly ball first, just like I hit slightly rail first when I use inside. Bob Jewett could comment on that but I think that is correct. Inside it is slightly rail first, outside ball first. Simultaneously may be a goal but is almost impossible, like a true split hit.