To diplex or not to diplex with your dish is a great question and depends on your signal strengths. If you are near your broadcast towers and have an easy reception situation, then diplexing can be a good idea. If your signal strengths are marginal, it can be a disaster to diplex in with your dish because you lose some signal overhead with the diplexers. IMO, it is better to keep the two antenna separate from the satellite dish. YMMV. Post your tvfool results and we can make a better assessment of your situation.
It is generally best to have the antenna level but there are situations where you can put an upward tilt on some antennas such as the Antenna Direct XG-91. Which antenna are you using?