Problem with "Material Planning in Networks"

I want to use the Mat. Planning field of an activity to do preliminary material cost planning as I do not know the exact cost of my components right away. Several months from now once Engineering has released a spec and we get a quote from a vendor we will add the component to the network and give it a real price.

According to F1 help of this Mat. Planning field, it sounds like exactly what I need:

• Tcode: CJ20N
• Choose activity -> assignments tab -> Mat Planning field
  
• The help says:
  

Perfect, that sounds exactly what I want.

To test, I did the following:

• Enter $1,000 in my Mat Planning
• Add a component to the activity:
  
• Run MRP to create requisition
• Set price of $900 in requisition

I then ran PS Report S_ALR_87013533 to check the planned costs, and this is what it gave:

• Plan: $1070 - O.K.(the 1000 I planned plus $70 which is an automatic 7% material overhead that the system calculates)
• Actual: $0 - O.K. (No GR or IR yet)
• Commitment: $900 - O.K.(I have a requisition for this amount)
• RemOrdPlan $1070 - Not O.K.? (I would have expected this to be 1070 - 900 = $170, but I'm not certain what RemOrderPlan represents)
• Assigned: $1970 - Not O.K. (i've only assigned 900?)
• Available: -$900 - Not O.K. (I have $170 available)
  

It looks like I have an overrun of $900, which is incorrect.

What did I do wrong? Why doesn't the expected material cost of $170 appear in this report? (Am I using the wrong report?)