I think that "so that" in your sentence would fit with purpose. However, purpose and result are not incompatible. A result can be unintended or intended. Purpose can be thought of as an intended result, i.e. a subset of result.

In practice, "so (that)" denoting purpose can be replaced with "in order that"

I eat, so that I am not hungry.

while "so that" denoting a non-volitional result can be replaced with "with the result that".

It rained, so that the ground is wet.

Edit: I misread the double negative at the end of the quote in question. I agree that it would fit with "result".

Purpose and result are not incompatible. A result can be unintended or intended. Purpose can be thought of as an intended result, i.e. a subset of result.

In practice, "so (that)" denoting purpose can be replaced with "in order that"

I eat, so that I am not hungry.

while "so that" denoting a non-volitional result can be replaced with "with the result that".

It rained, so that the ground is wet.
The birds return every year around March, so that April is a good time to see them.