If you look at details of all the calculations, you will see that what you override as QBI for the activity (e.g. Sch C) will flow through to Loss Netting and Carryforward as well as the QBI Worksheet.  However, QBI computations for the respective activities still show all the allocable deductions as if there is no override although these don't affect the actual QBID, which is an inconsistency.

FWIW, you may also like to refer to a recent thread here and judge for yourself whether you want to stick to this position: https://proconnect.intuit.com/community/Discussions-Tax-Reform/Proposed-vs-Final-Regulations/td-p/10...