Dear Quang,
Please check if you using A01 combination with R02, R09 or R10, then it is standard behaviour
to have it show as GI as this is hard coded and no setting can change this.
Another possibilities is transaction OMBA with wrong combination.
MIGO_GI assign to WE document type
MIGO_GR assign to WA document type.
However, i think your behaviour seems correct if you using A01 with R02, R09 or R10.
Regards,
ian Wong Loke Foong