Welcome to the forum, Steve, and thanks for the feedback. There isn’t, so far as I know, any way to influence the start position of the release in playback at the moment. The fundamental problem is that regardless of whether you notate the held note as a series of tied noteheads or a single notehead, internally Dorico is still treating that as a single note. Really the playback interpretation simply needs to be made much smarter, so that it takes into account the position of the end of the last notehead before the release note to decide the start position and duration of the release portion. I’ve made a note of this and we’ll try to address it in a future version.
I’m not an expert on guitar notation, but in the surveys we did when we were primarily working on guitar notation through most of 2019, we saw a lot of variation for all of these kinds of notations, and there seem to be a good many conventions in use.