Please forgive me, but I'm getting excited here... I may have connected some dots that were left unconnected before...
1: In "Ardashir and the Sasanians' Rise to Power" by Dr. @tourajdaryaee & "ReOrienting the Sasanians" by Dr. @sasanianshah I did not see these connections.
2: For some reason various sources note the name of a "Indo-Parthian" ruler as "Sasan", for example ...
in "Problems of Chronology in Gandhāran Art":
and "The interrelation between Indo-Parthian and Kushan chronology", 1992. This second article seems to provide some clues:
Achaemenid Royal Audience Scene, inside shield of Persian soldier on so-called 'Alexander Sarcophagus'
4th C BCE, from Sidon, @ Istanbul Archaeology Museums, Photos: Fluorescent UV & Reconstruction
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An older drawing without some of the details (1);
There are parallels, precedents to #Achaemenid royal scenes in Assyrian, Elamite, other Near Eastern art. Drawing in photo 2 for example is likely of an older, Elamite seal which continued to be used in Achaemenid court
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We see examples of this royal audience scene @ Persepolis, here reconstructed from the fuller image @ Apadana, and another modern recreation @ Zinat al-Molk House