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Thanks everyone for the suggestions.  I'll try and consolidate them here in a single post.

Ken - yes, one reason why I picked something so close to the Moon was that it was easy to eyeball the angle for initial setting of the index.  I estimated 8-10° so started at 10 and I saw Regulus immediately.

Alex - that is a great suggestion (holding the sextant upside down in the left hand).  I will add that to my list of skills.  Adding a folding chair is on my list, too.

Michael - I checked IE before I started, but neglected to check after I was finished.  I will add that check!  I used to do both, but I've been spending time with the iron chassis of a Kollsman most of the time these days and plum forgot.  Thanks for reminding me!

Frank - thank you for doing that analysis.  5' error is significant and a lot of it is likely me and inexperience with bringing stars to the Moon's limb, in general, and the issue with my inability to overcome the brightness of the Moon and losing Regulus in the glare, more specifically.  I was rotating the sextant to get separation of the star from the limb and then rotating back using the arc formed to judge a grazing touch on the limb.  I never saw the star touch the limb.

The good news is that the weather guessers were wrong about today's cloud cover (it is currently CAVU on all bearings) and I will see if I can take a better shot tonight. With the suggestions and encouragement found here, I hope to take a much better shot!

Thanks, everyone!

-- Art