Schedule B-1 is for a partner\s or entity owning 50% or more. 

I'm not an expert in the rules of attribution but I don't beleive it applies. 

but if attribution rules does apply this partnership you'd complete the information in Screen 5 - Other information - Schedule B

The rules of attribution do apply to partnerships. 

I think the best input for showing the ownership % including attribution is in Screen 32.1 Sch K-1 Miscellaneous using the input line for "Maximum percentage owned"