FNH, try raising the antenna up so the ends of the radials are at least 10' feet above the metal roof, and try and get the radial angle more steep, maybe down to 20* - 25* degrees from the mast if possible. Then you should be really good to go if you don't get bad reflection off the roof.
Corrugated metal looks ideal for mounting an antenna above, but that may just be the way it looks to the user, and not to the antenna. My experience says this roof material can be another problem that might not appear to effect the match, but might still seriously ill-effected the antenna response in a destructive way. I found such installs seriously attenuated real performance, and I think even 20' higher might get you well into the open enough to get better contacts. If we could see RF this would be easy to figure out, but let your senses guide you on the roof deal.
Also regarding the length of the stinger. I can't tell how long the feeding line setup that is exposed out side of the coax really is, but with that type of feed point construction you have to consider that the exposed wire outside of the coax is radiating, big time at that point, and IMO long is not good. It will be shielded inside of you mast pipe, but again it is hard to really tell what is going on in this case. If this length is no more than about 3" inches, then I wouldn't worry about it, even though you'll still have to figure it's a big part of the matching length for the radiator.
BTW, this 1/4 wave with proper horizontal radials should naturally show you a resistive match of about 25 ohms near the base, and angling the radials down tends to raise this impedance reading up not down.
The radial length should also be about as long as the radiator, given the diameters are about the same and the closer this is the better the balance is at the feed point...which is important also.
Good work and design, make the elements a bit larger the next time, and even old Mother Nature will talk bad about you.
Welcom to the forum, and keep us posted on your contact work, OK?
