Real Elements

[Elements]
-- Fire/water/lightning etc techniques are made from reiryoku exclusively, meaning that the technique takes the physical properties of the chosen element, but not the physical composition. This means reiryoku fire has fire's physical properties: it can burn, light up a place, crackle a bit. But it won't have its physical composition: it can't be doused with water, removing its heat and oxygen or air won't vanquish it, and it doesn't use oxygen to burn.

-- Therefore in an elemental battle, the chosen element are merely aesthetics and there is no elemental advantage over another because there is no core composition. It's reiryoku vs reiryoku.

-- If a reiryoku techniques creates something that has the properties or components of two elements, it would fall under elemental combinations. So you'd have to combine two different types of reiryoku to get a new effect (like water + wind = mist), and it won't have a low Tier.

-- With regards to elements that aren't made with reiryoku, such as those made with items, so long as its specified to be the natural element in its purest form (so actual real life fire), then it would be under elemental strengths and weaknesses that are present in real life, not the Bleach universe. So water > fire > wood.

-- As Soul Communication is controlling objects/substances in their natural state, it's treated differently:
Since it's reiryoku that's controlling these elements, the interaction with reiryoku forces the element to lose its physical composition but not its physical properties, and the moment it loses any contact with reiryoku would restore this. So in essence the reiryoku and element are used in synch enough that they mix slightly, and force this change to take place and make it to be near enough identical to the element completely made by reiryoku.