If you have redone the "VMCG" work for a deviation consistent with the reduced width, you can easily end up with a lower number than the "normal" 30ft deviation. It means having a faster VMCG to achieve the smaller deflections, but it's one of the possible tradeoffs to allow narrow runway ops. (There's still other considerations than VMCG; TCCA have an AC - 525-014 I believe - that details what THEY expect you to assess to qualify for narrow runway ops)