I can't speak for the rest of the fandom, I'm afraid. But for myself: on the recommendation of a friend I started at the other end, with the Harriet novels first, and then swung back around to the beginning. Parker doesn't have a very prominent role in the later novels, and consequently, I think my own shipping patterns were set by the time I'd swung back around to the beginning. I noticed the chemistry between them in those first novels, certainly, but coming from that end around it seemed more of an anomaly than a defining characteristic of the series.