Perhaps I misunderstand your question, but believe it’s as Olu describes above.
In the screengrabs Olu provided:
You’ll see that the dashboard form shows a split of 9:1 for 456.com to 123.com.
You’ll also see that in the API definition target list, 456.com is entered 9 times, and 123.com is entered just once. That provides the split. Let me know if that helps?