How does the shield of Sentry's Black Hole Sun ability work?

I'm trying to understand the details of Sentry's first ability. How does the shield of the Black Hole Sun ability work?
For example:
Shield 20%
Shield Health 600
Damage Conversion 65%
Maximum Damage 540
What are all these numbers? How much damage will I actually receive from an attack, and how much will Black Hole Sun's damage increase? Please, give a general formulas, or values of damage received and BHS damage increase for the following values of an applied attack damage: 100, 500, 1000, 5000.
P.S. The main reason to ask the question is that it feels like you can jump into shots and take a tons of damage with BHS shield receiving ~0% of it, so probably both shield and damage conversion reduces the damage? But how exactly? I would imagine that it is something like dmg*80%-min(dmg*80%,600)*65%, but I'm not even sure how I can test it.
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