In Odoo 18.0, this configuration:

- sent the first 50 received to 1A1

- the second 50 received to 1A1 

- the next 50 to Overflow

Incoming quantities are not split*, so after selling 50 from Overflow and 25 from 1A1, the next 50 was suggested to store in Overflow:

* to do this properly would involve another set of rules about when to split and when not to split:

• is there a minimum quantity before a split is suggested? (you would almost never split if there was room for just one unit)
• is the time taken to count and split and visit a second location less than the time it would take to just visit the second location when product is eventually needed again? (and also what if other Transfers are delayed because most Transfers using putaway rules now have two destinations?)
• is there a risk of damaging products? separating lots? damaging packaging? 
• who creates, updates and monitors these rules to ensure they aren't just adding complexity?