With the compound angles, you won't be able to make the two values match another value with only a single pivot.
That's also what I was thinking, expressed by my preceding the estimated upsweep #s with a "~". The upsweep will decrease as the backsweep increases, but not at the same rate (nor a linear rate), though I'd guess it's close. I'm just trying to confirm the basic relationship between angles, get a rough estimate of how they affect one another as the bar is rolled, and make sure I'm not overlooking anything (like compromising the bar's resistance to breaking).
Is this a hypothetical question? Or are do you think you can actually feel the difference between handlebars with those angles?
It's hypothetical but do think I can feel the difference. Like you, I micro-adjust a bar by feel, but have found I consistently roll a bar back until I dial out any sense of excessive upsweep, then stop.
For years I ran narrower 9/5 bars a bit rolled back, so maybe ~10/4 or ~11/3. Moving to wide bars, I briefly ran a 8/4 bar rolled to ~9/3 - it felt different, nice when standing, encouraged an attack position. Got a deal on a 9/6 bar and promptly rolled out that nagging upsweep, so guessing backsweep is at least 11*. More comfy, less aggressive, reach has shrunk. This bar is carbon with 38mm rise, so I'm keeping it, but sorta think I'd prefer less backsweep (life must be swell if these are my concerns...).