I believe that I got it!
: P
(not sure what’s the policy, mark as solved, remove thread altogether or keep it if someone may find it useful)?
What seems to have separated the spikes into islands is that I’ve treated the initial (now reproduced successfully) unwrap with ‘follow active quad’ (a tool completely new to me; didn’t assume that only quads follow quads (am I on the right track now at least?? : D )and drop the tris)…
the funky unwrap (now acting as expected, as far as the overall integrity is concerned) but with heavy distortion as a tradeoff:

distortion addressed, at the cost of a single continuous map being broken down into three:

Although the initial problem is somewhat solved, I would still appreciate any tips and suggestion on this (both specific and more general) kind of solutions from the people with more UV experience…
: )