Generally one doesn't use the full crossed position, even though the chain is carefully measured to make it possible. You're right in that the chain is coming from too far outside the bike (or the RD pulley is too far in). The extreme angle causes it to climb up over the side of the pulley.
Sometimes this improves if the hanger is straightened, since when the hanger is bent in (as it does if the bike is dropped) the lower pulley is inboard of the low gear sprocket.
Also it's possible there's a bit of twist in the hanger or cage worsening the problem. A worn pulley also worsens the problem, but before you spend a ton of dough be aware that often even with all three issues addressed the problem won't go away.
Best advice, do a quick check of the hanger (eyeball from the back of the bike), and if it looks good, and shifts well otherwise, simply give up riding this combination which you shouldn't ride anyway.
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