Yeah I see a problem. You ignored the listed instructions! Now, if that unit has any problems, the factory can wash their hands of it.
What can go wrong?
-fire, sooting, shutting off, odors, premature failure of components, and melted vinyl siding for starters.
Factories spend hundreds of thousands of dollars designing, testing, listing, and monitoring appliances. Here you come and want to throw all that out the window. The best part is, if there is ever an Ooops!, the opposing side can subpoena your computer records, including this list. You posted here you installed it improperly. You cannot ever erase emails and internet postings. There are companies that make a damn good living reconstructing your words.
Do yourself and the homeowner a favor--go back and install it correctly.
So what brand and model Fp is it?
They pitch up because it required it to pass the listing and to run properly. Condensation is not really a factor with gas direct vents under most conditions with short runs but it can be on longer runs. Actually, pitching it up pre-disposes it to rain penetration.
Hearthman