I would suggest NOT trying to install it in the "perfect" position, since that may be a moving target. Set it an inch or two forward of where you think you need it and take up any slack with minicell foam padding. This allows you to compensate for differing footwear, etc. I've had four commercial boats where I was forced to use the bulkheads for footrests and a couple of skin boats with fixed footrests. I can tell you from experience that if they're off on the short side, it can be a major pain. It's better to err on the side of extra length.