STO Inter-Intracompany code

Dear all,

There are hundreds of posts and i would like your help to clarify the STO process.

I have an Inter company process (NBCC PO, Outbound delivery, GI, SPED output type, inbound del GR).

If GR quantity > GI quantity then stock in transit is negative. Is this correct? How it is managed?

If GR quantity < GI quantity. Is it possible? How it is managed? GR for the whole quantity and then Return PO for the missing ones?

If materials are HU managed how return STO is possible?

Best Regards