For xDSL systems, alien noise cancellation using an additional common mode sensor at the downstream receiver can be thought of as interference cancellation in a Single Input Dual Output (SIDO) system. The coupling between the common mode and differential mode can be modelled as an LTI system with a long impulse response, resulting in high complexity for cancellation. Frequency domain per-tone cancellation offers a low complexity approach to the problem besides having other advantages like faster training, but suffers from loss in cancellation performance due to approximations in the per-tone model. We analyze this loss and show that it is possible to minimize it by a convenient post-training "delay" adjustment. We also show via measurements that the loss of cancellation performance due to the per-tone model is not very large for real scenarios.