killaling:

Cost of goods manufactured, is a component of Cost of Goods Sold (COGS).  It is NOT the COGS. 

Therefore if you produce less, you will tend to draw more from your remaining inventory when you record a sale.......hence a charge to the profit and loss statement resulting in a reduction in your GP%. 

The other way around.....when you build inventories, increasing your cost of goods manufactured while at the same time replenishing the inventory that you are drawing, your GP% increases. 

Whenever you produce more than you sell, your capitalizing the costs of production to the balance sheet...hence no charge to p&l.  This questioning how the change in inventory affects your profitablity.

Hope this helps....