But what was the tracking set to?
^^^ as above, what are the settings?
your car would benefit from more 'toe out' at the front to overcome the issue. just depends what the toe is set to currently.
other issues can come into play too (incl what has been discussed), so MORE INFO about your car would be helpful. some of this stuff obviously can't be overcome though:
*tyre size: low profile, wide tyres are more prone to 'tram lining'
*ride height: lower, stiffer cars are more prone
*stiffer antiroll bars: will contribute
if everything is 'standard', and the toe is appropriate, there's probably nothing you can do about it. it is of course subjective; meaning, what you have could be quite acceptable and normal to other people, so it's a little difficult to know how much, if any, problem you actually have.
ideally, you would drive a similar 156 to compare.