My Syncretism of Astarte is as follows:
She stems from Inanna and Ishtar, so of course, their essence is also her essence. They are her, yet she is them, but they are certainly also separate at the same time. The energies of Inanna and Astarte feel quite different. Inanna feels much more warrior-queen esque, whereas Astarte to me feels much like a loving mother goddess. Ishtar is right in the middle.
I also feel Astarte, at least in her names Astarte and Ashtoreth, are heavily interwoven with Asherah, which is why I get that Great Mother essence from her.
Through her identification with Tanith, I syncretize her heavily with Diana, on top of that Diana of Ephesus is very likely a variation of Astarte, Kybele, and Atargatis (all of whom are identified with eachother).
Furthermore through the syncretism of Astarte and Ariadne in regards to being part of that Great Mother lineage, she can be likened to Arianrhod, who I also identify with Aradia and Diana.
And then, I theorize, Andraste herself may be a British form of Astarte. They have very similar names, and very similar roles in regards to not only being warrior goddesses, but also goddesses of fertility and the moon. Especially with Astarte having been worshipped in Britain by name and with the title Caelestis.
And from all of that, I identify her as The Witching Goddess. Who is also Aradia, Diana, Andraste, Rhiannon, and Arianrhod.
Shes so many all at once, yet she is herself.