Do YOU pronounce Sigil with a hard or soft G?

[Xuc Xac]

I quite assure you, that the way a lot of Midwesterners pronounce "SCUBA", the "a" at the end sounds just like the "a" at the beginning of "apple" (at least with our pronunciation of "apple", anyway).

Cool. Prove it. You'll have to provide a recording of someone who talks like that, because I lived in the Midwest (and traveled all over it for work) for decades and never heard an accent like that.

It's possible that there's some small pocket of people somewhere who say /skuː bæ/ instead of /skuː bə/ or /skjuː bə/ like everyone else, but I think it's more likely that you just can't hear the difference in those sounds. It's also possible that you're over-emphasizing the sound and pronouncing it differently when you test it than you do in normal use when you're not paying attention to it (like saying "thee" instead of "the" when you stress it).