So, at the advisement of the GM, I'm going to write down some of my theories for how this all works.
My best guess at what order runes go in is thus: Vector-Substance-Method. Alternatively, Where-What-How.
To elaborate, working backwards, the Method/How is what kind of effect the magic has. So, like, in Black Dragon's Lethargy, the Method is Attack(Fire), which results in the aggressive 'devouring' (fire) of stuff. In Reinforcement of Cutting, the Method is Attack(Shadow), which results in aggressive separation... I think.
The Substance/What is what the magic happens with. In BDL, the Substance is Form(Water), so the stuff is 'devoured' by creating water. In RoC, the Substance is Form(Air), which (I think) means that the way the separation happens is by creating air- I think that RoC works not by making the physical blade harder, but by overlaying a 'blade' of air.
The Vector/Where is to what/through what the magic happens. In BDL, the Vector is Ward(Earth), so the stuff that is devoured by creating water is vitality (earth). In RoC, the Vector is Ward(Wood)... which I think means the separation by creating air is applied to a living target...?
However, this is obviously not entirely correct. When we asked about making a fear-causing spell, the hint results indicated that the first rune had more of a How effect than I thought- indicating that the use of a Water rune would 'drown' the fear, and a Fire rune would 'burn' the fear, whilst we needed a rune to 'grow' the fear.
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We have information about what the various elements do, or at least a rough description, but the only thing we have for the meanings is what shape they have (super useful). The only meaning whose... meaning I have a good handle on is Form- Form(Stuff) means to create stuff, at least it seems to in many cases. Hopefully attaining Form Mastery will either confirm or deny this.