You need to understand that the ruler on top perfect angle requirement that you sdp, and Stevenson are looking for is ultra rare. The real world is not perfect. Most guys in the world have not heard of this and not all these requirements are 'official' rules to measure a dick, therefore they are not performing it.
The typical guy who measures his dick in a quick photograph to show off will just pull out a tape and measure his dick erect from any angle or position to show someone, he does not know what this 'perfect' measure requirement is that you keep requesting or any of the other things you mention.
There is a serious lack of ruler measurements out there over 9 inches, but many tape measurements. I think this subject is more simple than you have made it out to be, a man measures his dick and that is it. You are expecting too much from people and being too critical. I appreciate healthy skepticism but you are taking it too the extreme.
You want an absolute perfect measurement from an absolute perfect camera angle and an absolute perfect position, it is requesting too much. Which guys in the world are really going to do this, just to please you? I believe this is just a way that you can downplay people, because you know hardly any men out there will be performing a measurement like this, so you can just keep saying every man is under 9 inches.
Whats my own opinion? As long as you can see all the numbers on the tape or ruler and where the ruler or tape starts, then the angle really makes no difference to me. I have measured my own dick with a ruler and a tape and I get the exact same number, I have measured from different camera angles and I still get the exact same number on the tape.