Thanks, Ben.
This question suggests a misunderstanding of how recipe scaling works, as the number of turns is irrelevant to the total quantity required. Whether a stage is multi-turn or not has no impact on the quantities of ingredients needed.
Adding turns doesn’t “scale up” the quantities required. When building recipes, ingredient quantities should always be entered as the quantity required for the recipe batch size. You should not adjust the ingredient quantity for the number of turns that you expect to do when brewing a batch using the recipe.
We have a full help guide on Batch ingredient scaling which might be worth a read.
In light of how recipe scaling works, I think you just need to use a single fermentation stage (as is already possible) and would benefit from Calculated ABV on merged batches & OG on multi-turn batches.
Can you let me know if you agree and we can close this thread, or if there is still something else needed? Cheers.