If you stretch and stick 13, 14 first, you're preventing the ability of stretching the cloth from corner to corner first, by only being able to stretch from the center to the corner. That means the center if the clothbis only stretched in length, and not side to side as well. Get your corner pocket grain of cloth pulled back and straight into each corner before you stretch for length. Then when you do stretch for length, all you need is a straight back pull, and it's much easier if you start that pull close to each corner pocket first, working your way to the center of the slate, you have more leverage that way.