Offtoa uses many of your stated assumptions to compute the value for your inventory, so any of these could cause the value of inventory on your balance sheet to seem higher than you expect:

1. Production Days. The higher your production days, the higher your inventory. For example, if you add 30 days to your production days, you should see all your inventory values (annual and monthly) increase by one month's revenue.
2. Average Days in Inventory. The higher your average days in inventory, the higher your inventory. For example, if you add 30 days to your average days in inventory, you should see all your inventory values (annual and monthly) increase by one month's revenue.
3. Waste/Spoilage. The higher your waste/spoilage, the more raw materials you will need to purchase, and thus the higher your inventory. For example, if you increase your waste/spoilage from 0% to 25%, you should see all your inventory values (annual and monthly) increase by 25% of one month's revenue.
4. Price of raw materials. The higher the price of raw materials, the higher your inventory will be.
5. The amount of raw materials you use in each product. The higher percentage of each unit of raw material you purchase that you use in each product, the more inventory you will need to maintain in order to sell the same amount of product. For example, if you change the amount of paint you need for a final product from 20% of a gallon of paint [a raw material] to 25% of a gallon of paint, you should see all your inventory values (annual and monthly) increase by 5% of purchased cost of a gallon of paint times the number of gallons you need to use for each month's sales.

Related Question:

Why are my accounts payable higher than expected?