WSF works by copying 'most' of the recipes in the game and adjusting the values by a multiplier (with some sanity checks) and having only those work in only the WSF factories that are randomly generated on world load. Those recipes do not need to have permutations performed and by doing so it is almost doubling the amount of recipes in the game, which increases load. These recipes can be identified by either having the postfix of -big in the name as well as they are assigned to one or more of the categories of big-smelting, big-recipe, big-chem, and/or big-refinery (with potentially more added over time). Skipping these recipes is both useful since there are only ever one of such factories anywhere near to another at a given time, and it would mean not doubling the amount of recipes in the game near outright.

I will look into it.

Alright, I went and implemented this. And as I started testing, I saw that I cannot reproduce this. Perhaps I do not have the correct mods - I tried with "Angel's Petro Chemical Processing" and with "Bob's Metals, Chemicals and Intermediates". They do not add recipes that have more than one fluid in the ingredients and/or the results that Whistle Stop Factories generates a big version of. And since this mod only generates permutations only for such recipes (with multiple fluids), the mentioned situation did not occur. Perhaps another mod adds such a recipe. Maybe you could give me the name of such a mod?

I don't know exactly what the performance impact of having more recipes is, but I am inclined to think that outside of using a bit more ram it is very small. Even if it has some impact, the recipes that are both suitable for WSF and for Fluid Permutations are a fraction of all the recipes. So even if Fluid Permutations skips all the recipes generated by WSF, the difference will be negligible.

Also note that all the recipes generated by Fluid Permutations are hidden and you will only see them as the selected recipe in a building (after you have "rotated" the recipe). They are in a separate group and if somehow you see them they will be under the "Fluid Permutations" group (it has the same icon as the mod thumbnail). So if you are seeing multiples of a recipe outside of that group - it is not this mod that is causing it.

I will try to reproduce this again, even if I have to create a brand new recipe to satisfy the conditions for both WSF and FP. And if the code works I will probably release the changes (I have implemented them with a setting, mirroring the current behavior by default).