Does anyone know how Mark positioned the shot line tape?
When I setup the shot line tape, I put the tape on the floor approximately, then I place the cue on the table with the tip at the base of the cue ball and the cue along the shot line, and I compare to the tape. Then I make adjustments to the tape position. I do that a few times until the tape is perfectly aligned (by my sight!) under the cue.
If you are also asking about the second parallel piece of tape for the left foot...
Mark recommends that the left foot be placed forward of the right foot and to the left of the shot line--with the feet "at least a shoulder width apart". The left foot is parallel to the shot line, while the right foot is perpendicular to the shot line. He also recommends that the left heel be further left than the back of the right heel. So if you started with your heels touching so that they formed a right angle, with your right toes up to the edge of the shot line tape, you could slide your left foot forward, say 10 inches, then you could slide your left foot to the left, say 6 inches.
He also recommends that your weight be distributed approximately 50-50 ("no more than 60% of your weight on one foot"), and the right leg should be locked straight (English style) or both legs locked straight (American style). He says to choose English v. American based on what you prefer after trying both.
I discussed this with another well-respected instructor and I think it comes down to one size doesn’t fit all. Like my instructor friend said, “Mark is 6’7” and does yoga, you know.” I’d guess that Mark would actually agree and makes reasonable allowances for different physiques when giving personal instruction.
I didn't get that impression from the book. He seems pretty adamant about his recommended stance--for all body types. There is some leeway in how wide the recommended placement of the left foot is: "at least shoulder width apart". However, he repeatedly says that comfort is not something that you will initially experience when practicing his stance. He claims that after you practice any stance for long enough, it will feel comfortable.
His main point throughout the initial chapters, which cover the fundamentals, is that you can use other stances, grips, etc. and still become a great player--it's just that it will take you much longer than if you had adopted his orthodox recommendations.
I hate to say it, but one day of trying left me fairly crippled for a week. I’m not hung up on “comfort,” but my flexibility is probably below average even for someone my size and age.
Same here--for a few days.
I just changed my grip to his recommended grip. His recommended grip is extremely loose with the thumb only preventing the cue from falling out of the curled fingers. The thumb points down, and there is lots of space between the top of the cue and the palm.