I'm going to quote directly from our own "Mini for Dummies" section. Where we talk about the differences in the wheelbases.

Some people will tell you that they handle differently, they don't really. Its purely personal preference, nothing more. Any handling differences are no more than you can alter yourself through set-up. There is NO significant difference.

And it's true.

Your problem is probably in your suspension and/or steering setup, it's nothing to do with the wheelbase.