I have a rather long series (currently only in volume 2 on Tapas but already in volume 7 overall) and I'm posting all the volumes in one 'novel'.
As far as I've seen from previous discussions there are some pros and cons to both approaches. To me ease of use was the one that stood out as the big advantage of the approach I'm using: Readers don't have to click around for the next volume and can just continue to read if they liked the previous volume(s).
The main disadvantage I heard about are the ominous 'dead subs' aka readers that sub but don't really interact which are supposedly bad for your statistics (so making it harder to get onto trending). Then agan, michaelson said in some other thread a few days ago that the 'dead sub' problem wasn't as big as we made it sound here in the forums 
So I guess in the end, it just boils down to preference. I like keeping my volumes in one novel and don't even change the icons for it (although I did think about doing that). I just indicate in the description box where one volume ends and another one starts.
I mean in the end, it's not really that important, is it? Readers can just read it as one series. The installments are more of a separation we as authors make when we're talking web novels.
Edit: Maybe in your case, you could try using the symbols in a differerent color for the new volume? If you want to visibly set them apart, that is.