Hello Mohd,
Co product Movement type is 101 and By-Product movement type is 531, and It is Standard SAP behavior its not depended on the Quantity size.
When you select the Co product in material master, you have to select the Co product filed in BOM item otherwise system material as By-product.
Please refer below document for your reference.
Co-Product and By-product in Production order
I hope this information helpful to you
Regards
Umesh Mali