Purpose of Extended Cost When user rolls up the cost

Summary: Hi Team, we are using Standard cost for Manufacturing items and having cost profile setup to cost these items in Secondary UOM called as MSF (Thousand Square Feet). We are seeing incorrect Extended quantity calculation for FG item while rolling up the cost.

Scenario:
Item - AGFG1000081
Batch Quantity – 1 MSF
Quantity Used - 29.856250 Pieces
Work Definition Cost Processing Batch Output Size – 1
Extended Quantity - 2,866.82573
Per Unit Cost - Extended Cost/ (Quantity Used*Costing Batch Output Size/Batch Quantity)
2,866.82573/ (29.856250*1/1) = 96.02096m MSF (Thousand Square Feet)

Questions:
1. We are seeing Extended quantity is calculated as (Quantity used * Per Unit Cost). What is the purpose of Extended Cost When user rolls up case, unit cost is calculated correctly but extended cost is not getting calculated correctly. Unit cost gets calculated for each MSF and then it multiplies by 29.856250 to get extended cost (Pieces) ?