We always advocate setting up a Wort BOM for each brewhouse. Usually the recipe doesn't scale proportionately between two different batch sizes, so you need multiple wort items and boms.
Lot's of customers have done things like this:
Item Code: W1005-S
Item Name: Wort - IPA (7.5 BBL)
Item Code: W1005-B
Item Name: Wort - IPA (30 BBL)
Then have a bom for each of those items for the specific batch size.
We usually suggest to not put numbers in the item code (like this W1005-30) where the 30 represents the brew size. It's better to use S for small or B for big, etc. This is because sometimes the bigger batch may start to be done in 35 BBL batches or 38, so it doesn't make sense to have "30" in the code.
If the smaller wort only goes into smaller fermenters, you could setup green beer for those as well, with the same logic (ie GB1005-S, GB1005-B). You only should do this if you specifically use different fermenters for the smaller brew house and larger brewhouse.
Also note, if all your recipes are already for the larger 30 BBL brewhouse, you won't be able to update the item code to put the "-B" on there. So you'll have the original codes, and then have the new codes with "-S" on the end for the new smaller wort items.