Former Scotland star Ferguson moved south of the border for the only previous time in his career when he joined Blackburn from Rangers in August 2003.
A serious knee injury curtailed the impact he was able to make at Ewood Park after he was signed by Graeme Souness before he eventually returned to Ibrox after 18 months.
But Ferguson is adamant he made a big enough impression when he was fit ahead of City's Carling Cup clash at Southampton on Tuesday night.
He has quickly adapted to life at St Andrew's and has been one of Birmingham's best players during the opening three Premier League games from which they have collected four points.
Ferguson said: "I have not got a point to prove. I enjoyed it at Blackburn. I started off well but then I got a bad injury. I fractured my kneecap and I was out for seven or eight months.
"I came back from it and I played a lot of games for Blackburn. I did well. I was captain there and, even though Mark Hughes came in (to replace Souness) everything was fine.
"But it was a case of 'when your old club comes calling' so I kind of left under a bit of a cloud."
Ferguson added: "I could have stayed, got a contract extension, joined other clubs who were interested, but I made my decision.
"People ask me 'do have I any regrets?' but things happen in life for a reason.
"I went back up the road to Rangers and I won more Championships, Scottish Cups and League Cups and got to a UEFA Cup final so I don't think it was a bad decision!"
Ferguson has settled into life at Blues after the unsavoury end to last season when he was banned from playing for Scotland after off-the-pitch incidents.
He said: "I am enjoying myself here. I am quite surprised how well I have settled.
"I am enjoying my football and that is the main thing. I think the last few months of last season were the hardest in my playing career.
"Now I am enjoying myself and it is a new beginning for me.
"I think the best thing that happened to me is after I signed is the following day we travelled to Austria on tour so I was with the guys 24-7 and that helped me and I got to know everyone pretty quickly.
"I've never had a really good pre-season myself results-wise and I think there were a few people worried after our results.
"But we played well against Manchester United, deserved to win against Portsmouth and did well at times against Stoke. Now we aim to do well in the (Carling) Cup."
Ferguson admits the chance to work again with City's former Rangers and Scotland boss Alex McLeish was a major factor in him moving to the club.
He said: "Obviously I played under him for Rangers and Scotland, and I enjoyed it. I like the way he manages and I know what he expects of me at Birmingham.
"He is a passionate man, a bit like myself, who wants to win every game. Working under him before was a big pointer in me coming here."
McLeish, who is hoping to complete the signing of Sporting Gijon midfielder Michel, may make changes after three league games in the opening week of the campaign.
He will check on the fitness of striker Cameron Jerome and defender Gregory Vignal who missed the goalless draw against Stoke because of ankle and hip problems respectively.