I must notice for all his Imperial-ness Imperial options max out at -2 and it's non-imperial one that shows -1 for all it's probability to fail.
Because it's pretty much "it's easier to beat disunited barbarians" (which is in line with Imperial ideology) "we need to recover first" (which is in line with Imperial ideology) and "barbarians are people... and maybe some are not barbarians" (which is pretty much anti-Imperial) and it's third one that can make him change opinion.
Let's be clear, the parts of option 3 that could sway him are not the bits where we advocate the wonders of friendship. Given this -
Cao Chun's reputation was as a hero, who had struck down many villains and saved many people, a man of unimpeachable virtue and great devotion toward the great spirits. However his reputation is also as a merciless foe of those who would cross Imperial law.
it seems clear that the bit we would use to
convince him to listen to us would be
this-
[ ] Be open in your intention for friendly relations and exchange in the long term. Discuss the White Sky where you can emphasizing the similarities over the differences. Use implication of Great Spirit interest and Ling Qi's patronage of the moon as legitimacy for the project. (40% chance to reduce opposition to your progress and swaying Cao Chun. Sets his Bond to -1 on Success or -4 on failure.)
at which point we would use that bit of borrowed authority to get him on board with the idea that we shouldn't treat our diplomacy partners as subhumans, in
spite of his Peakaboo inclinations, because the Moon seems cool with them.
So the +1 to personal rep would mostly be from our Great Spirit Patronage, which we would use as a wedge to push for the reduced project opposition.
As for which option we should take, a -3 with our imperial attache is survivable while a -4 is
far less so, so I'm thinking we go with option 2. Pushing for the full power of friendship later will be difficult, yes, but if we can build our personal rep via accomplishments or build our supposed Spirit backing via Ling Qi shenanigans, we should be able to take another crack at him then.
Worst comes to worst, we can never bring him around and he just contextualizes any "friendship" that might come up as a distasteful but effective ploy to secure borders and a source of metal imports, which is the best I think we were expecting from the Peak anyway.