Unable to select Same Item classification for Different Tax Category

Tax Category defined for Item Classification as RMIN with CGST and SGST, But if want to attached IGST as default Tax category for same OU then Not allowing the Item classification as RMIN.

Example:

1. If there are 2 items I1 and I2 having different HSN code, so the Tax % may vary for the items . It can be 14% for I1 and 18% for I2. I have mapped HSN code to both the items which can only be done through Item classification:- in Below screen Item classification is mapped to HSN Code in reporting structure.

2..Now I want to include I2 in the same screen and it is allowing to do. But my tax category for this will be 18%