93,
"When using the ritual to invoke a single element, I use the active or passive spirit-pentagram first with the appropriate enochian spirit-name and then the hebrew god-name, then I use the invoking-pentagram of the element in question with the appropriate enochian vibrations. I do this in all the quarters."
I would recommend you research the origins of this ritual and where it first appears in the original Golden Dawn context, and then question what it's most appropriate use is. A lot of people utilise this ritual to invoke one single element, however, it is common practice these days to utilise the lesser ritual of the pentagram for this purpose.
As for the Enochian spirit names, I personally don't mix them up with Hebrew at all, nor does Crowley in his instructions in Liber O. I feel as though this is a Mathers addition rather than the traditional edition. Nothing wrong with that, but you may want to look into Enochian work before utilising the names within that system. It is not the light-hearted.
"When I get to the part where I affirm the presence of the archangels (before me Raphael, behind me Gabriel etc.), have I not really evoked Raphael (if I am working with air) in all the quarters? Should I not rather affirm the presence of Raphael (if working with air) in all the quarters ("Before me Raphael, behind me Raphael" etc.), or is there a good reason to stick to the "balanced" configuration of archangels, even if I am working with only one element?
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This is where confusions arise and debates are evoked. In the original ritual context, all archangels are to be utilised. When I was experimenting with this ritual to invoke a single element, I personally didn't say "Before me...etc." I simply vibrated the appropriate angel name and visualised it in front of my altar or in the appropriate quarter. I'm not saying this is what you should do, rather, it was what I found effective personally.
I'm sure others will have alternative responses and I am interested to hear them! Hope this helps in some way.
93, 93/93.
Mark.