Requirement type determination in sales orders

In SD, the requirement type determines a number of things (via requirement class) , including special stocks. The configuration for requirement type is in the following node:

Sales and Distribution -> Basic Functions -> Availability Check and Transfer of Requirements -> Transfer of Requirements -> Define Requirements Types or TCode OVZH
Sales and Distribution -> Basic Functions -> Availability Check and Transfer of Requirements -> Transfer of Requirements -> Define Requirements Classes or TCode OVZG.

The determination of the requirement type is a convoluted series of steps, and an understanding can help if you are puzzled how the requirement type was picked up.

Step 1:
First, an attempt is made to find a requirements type using the strategy group in the material master (MRP 3 view) Strategy group configuration is in the following node: Production > Material Requirements Planning > Master Data > Independent Requirements Parameters > Planning Strategy > Define Strategy Group (TCode OPPT) Strategy group is assigned to a strategy, which is assigned to requirement type in the node below. Production > Material Requirements Planning > Master Data > Independent Requirements Parameters > Planning Strategy > Define Strategy (TCode OPPS)

Step 2:
If the strategy group has not been maintained in material master, the system will determine it using the MRP group Determine strategy group from MRP group (in material master MRP 1 view) Production > Material Requirements Planning > MRP Groups > Carry Out Overall Maintenance of MRP Groups (TCode OPPR)
Continue with step 1

Step 3:
If the MRP group has not been defined, the system uses the material type instead of the MRP group Determine MRP group from material type in the following node. Production > Material Requirements Planning > MRP Groups > Define MRP Group for Each Material Type (TCode OMIG)
Continue with step 2

Step 4:
If no requirements type is found here, the system assumes a special rule and attempts to find a requirements type with the aid of the item category and the MRP type. The configuration is in the following node: Sales and Distribution > Basic Functions > Availability Check and Transfer of Requirements > Transfer of Requirements > Determination Of Requirement Types Using Transaction (TCode OVZI)

Step 5:
If this is not possible, a last attempt is made to find a requirements type with the item category only. From item category and blank MRP type in the following node: Sales and Distribution > Basic Functions > Availability Check and Transfer of Requirements > Transfer of Requirements > Determination Of Requirement Types Using Transaction (TCode OVZI)

Step 6:
If the last attempt fails, the system declares the transaction as not relevant for the availability check or transfer of requirements.