A score of 652 at approval and at 657 more than 9 months later is not "rising." Frankly, the OP need to figure out and address the reason(s) why their score might be stuck in a narrow range whether it is high utilization, derogatories on their report, or whatever the reason is. While Amex sometimes takes a chance on applicants with "Fair" credit scores the expectation is that those scores would enter in the "Good" range before credit limits are increased.
@Brian_Earl_Spilner wrote: See, that's kind of dumb. Your score was good enough to be approved and it's rising. Why quote score unless they feel you haven't improved enough for more money. At that point it should be "not enough experience at current limit" or something like that.