Not sure if you're the same person who posted this on /r/frc, but I post the same advice that the commenter over there gave.
http://i.imgur.com/nrzXmTA.jpg (you may have to zoom out)
"[You] can bracket the front from the mounting holes (arrows). Doesn't need to be parallel to the ground, but does need to cover the front corner."
You should be OK having the bumper angled up with the front of the threads as far as Robot rule 4.2 R2 goes. I believe bumpers can be 4-12 inches above the ground, if I am not mistaken.
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