Defeat, courtesy of Tom Pope's brace, was City's third in six home league games, stark contrast to their away form where they have won four out of five.
"I'm disappointed," Tisdale said. "Port Vale are a good side and they are the most effective team we have played so far this season and we are just short at the moment.
"I am not going to get too downhearted, it is a quarter of the season gone now and a good time to assess our performance and we have not been effective enough at home.
"I have to look at the reasons why and we have to look to improve from here. I am certainly not going to get too despondent about it. As much as I am unhappy with the way things ended up, they are a very good side and very effective. They know their game, they will be a good benchmark for us.
"I would say that on another day we could have got a result, but they are a strong side and it is a good barometer for us for the next quarter of the season."