… for example… continue please, so far I agree wi ye.
Well most obviously, context. Havnt found any pieces reflecting a Carribean theme. 
& of course, technical mastery. I would… humbly…and cautiously… assert that the B section has continued to TEND to favour the upper register, AND stress a fewer number of tones (in other words, circling around high F#, G, A, or B); as opposed to introducing newer, more contrasting, or aditional melodic ideas.
But these are all merely surface observations; exceptions are expected.
On a deeper level, (sorry if losing some) the ‘golden mean’ porportion TENDS to becomemore important in recent interpretations. Concious or uncoicious choice, inherent or artificial, I cant say. Just a casual observation of tendencies.
Given that tens of thousands of Irish where transported there after the War of the Three Kingdoms and the Jacobin rebellion (Hell Connaught or Barbados) I would be surprised if’n ye didnae discover some Caribbean Slow Airs 
ye are not wrang in your observations.
I think the Golden Ratio is a valid point to raise given it would point to perfection in both hearing and appreciation.I think it is probably more or less intuitive,possibly genetically embedded, on the part of the player which then transposes to the listener who will pick it up intuitively.Your observation on glissando and a rising B part would point to a Golden Ratio or at last a part influence of same 
“I am comparatively studying 27 slow airs recorded over a 60 year period”
Tell me, is this for your own edification, or are you writing a paper?
Cabbage!!! Lots of it!
For what it’s worth if, while playing a slow air, I experience a physical symbiosis of body movement with the various phrases, rising and falling with a natural rhythm, catching a musical breath here and there, gliding along naturally, unconscious of technique that, for me, would be a “good” slow air.
That twould be your body reacting quite naturally to the Golden Ratio methinks…tis the same if ye listen to a particularly evocative piece of classical music eg Pietro Mascagni Cavalleria Rusticana - Intermezzo
note the body movements of all those involved..pure simpatico with the Golden Ratio…beautiful.
Now then if ye can play a slow air and evoke the same feeling then ye can safely say ye are playing a slow air and not think ye are.
http://www.youtube.com/watch?v=7OvsVSWB4TI&feature=fvw
To not experience some emotional connection with the piece would mean I am afraid that ye are dead…or simply not human 
Uilliam