DMAAI 4315, B line type and flex accounting

The user is successfully flexing in business unit on other line types, but the B line type is defaulting the business unit from the purchase order header. The GLC is being populated in the F4211, but it still pulls from the header.

Is there a stocking type that can be used with a B line type that will use the item branch GLC to flex the business unit? Or will B line types always pull the header BU?

Thanks!