Currently, the Infuser requires to be surrounded by air blocks to function.

This seems to be an artifact of a feature from when it was ported, when in practice, this feature seems cumbersome, confusing, and serves no functional purpose as currently implemented.

Understandably, a clear path to the soul sand needs to exist so spirits from smashed bottles can travel to the soul sand. This feature should be preserved.

However, a hard requirement of the air blocks leads to confusion and clunkiness when assembling the Infuser multiblock. One, it's difficult to convey that information to players (this is just true of most multiblock structures). Two, it severely limits the ability to incorporate the Infuser into player builds, homes, and bases.

The recommendation is to completely remove the requirement of having air blocks, soul sand, and light level in order for the Infuser to function at all. The Infuser should simply function when placed down, and only make checks for light level and spirits for individual crafting recipes.
For example, if modpack makers add a recipe to the Infuser via CT where the recipe requires ZERO spirits and can be crafted in any light level, then the recipe should work even if the Infuser isn't on a block of soul sand at all, has blocks placed around the table, and the sun is shining down on it.
However, if a recipe calls for 100 spirits and complete darkness (0 light level), and a player tries to craft that recipe with 50 spirits and a light level of 3, then the recipe simply doesn't output. But a recipe calling for 20 spirits and a light level of 2 would.

Remember, even the vanilla enchanting table works if its placed in a dirt hole and not surrounded by bookshelves. It's just limited in what you can enchant.

btw this will come maybe at a surprise but even the vanilla enchanting table needs an arbitrary airgap to power up from bookshelves, so at the very least it's not arbitrary, the bookshelf and the airgap are just in different places :p

Sure, but if you place anything between the bookshelves and enchanting table, it doesn't cease to function entirely - you just don't benefit from the obstructed bookshelf. At least the air blocks make sense with the enchanting table. They do not for the Ancestral Infuser. They should be optional for the purpose of smashing spirit bottles and nothing more.