More info needed, basically.
Different missions have different effects. Influence rewards are tied to credit rewards, and as such a majority of Odyssey missions don't give more than + or ++, because their payouts are rarely worth more than 200-300k, while a +++++ inf mission needs at least 1.5m in rewards usually... which most space missions are.
There is also a bug which was thought to be a display bug, where all mission submissions give just + inf... maybe that isn't just a display bug.
But yeah, it's hard to say Odyssey gives less without knowing whether you're comparing like with like.