Thanks for the clarification,
platformHeading seems to be what I was looking for.
As for the other two parameters: I didn’t realize that these were purely SNAP parameters, assuming they had to be constructed somehow from the product metadata. However, neither the Java code in the snap-engine GitHub nor the documentation from the SNAP Developer Guide provided any conclusive information on the abstract metadata section in SNAP.
Consequently, my comment regarding metadata descriptions is rather related to SNAP / Sentinel Toolboxes rather than Sentinel-1 itself. I think that a documentation of the SNAP metadata parameters would be helpful, as this could save both time in looking for plausible answers and making assumptions on what they could possibly mean.