Hi alik — I vary my angles, but mostly perpendicular. I read one place that suggested if there was only one angle, choose perpendicular. I believe perpendicular is more apt to equalize tension across front/back & sides for an even stretch. However, if you want to focus on front/back or either side, you can do that through angles and tension bar settings. I think that just comes down to what you’re after, and what is your focus.
I also have a slight bend upwards, and want to keep it. I haven’t read anywhere that the stretcher will change the upwards bend, but obviously many use it to correct the sideways bend. Good Question! Hmmm.. Just thinking from mechanics, if you were to stretch in the upwards position (toward belly), I would think slight more tension would be applied to the underneathe as opposed to top, thereby favoring the upwards curve. Just a thought. Sorry I don’t have a conclusive answer on that.
My BPFSL is also longer than BPEL. When you do the BPFSL, give it a nice gradual yet strong tug (perpendicular). So gradually pull out with some force to point it won’t stretch any further, and although you feel the pull, it’s within comfortable limits. Also, make sure your grip (thumb & index finger) is right below the glans (which is part of the measurement), and make sure the glans is pushed outwards for a true measurement. Also make sure your point of measurement for BPEL & BPFSL are from the exact same point. I realize some of this is obvious, but perhaps it’ll ignite a light bulb — Awwwww… :)