I feel that in this very example (TLV AMMOS 1E followed by the RNP W 30) things are quite clear: We usually get a clearance like: "Descend to ALT 6000ft via the AMMOS 1E ARRIVAL" - so we will to descend to 6000 ft respecting all the constraints on the arrival. At some point they will say "You are cleared for the RNP W 30", so we follow the ARRIVAL to HADAS, and as HADAS is not only the end of the ARRIVAL but also the IAF of the RNP Approach as well (and we are cleared for that approach), we can now follow the cleared RNP Approach which allows us to proceed to the runway and descend according to the procedure as well (HADAS AT 6000FT, MORIA at 3600ft, ROMIE at 2400ft, BG005 at 1800ft).
Thats how we do it every time and I would say itˋs quite straightforward.