since, v2.3, by default, VTAs are calculated in native space and warped to MNI. Thus, what you see as the deviation is the nonlinearity in the warp. Instead, the electrodes are modeled as a line always (at least currently). Thus, fit around the contacts is nice but not throughout the whole lead.
You should not see such a deviation in native space.
Re new topics, I guess the forum is a bit buggy and also much more buzz is in the Slack channel. Use that one instead, there are also way more people there to provide help.