For standard cost your cogs should equal the standard cost
Actual costs may be different, and should go to variance as a below the line margin gap, and not be added back to cogs. Your standard will typically be a little higher than expected cost at the start of the year and a little lower at the end of the year - and the plus and minus variances should set off against each other- it will not be perfect when the variances are one sided, then its time to revise your standard.
The point of standard is to treat sales and production as separate - sales know the cogs in advance and can quote with confidence without the changes in month end margin shocks they may get with other methods. They don't benefit from favourable runs and they don't get penalised with unfavourable runs. Production need to account for variances, but those are outside of cogs, which are based on a standard which expects some variances.
Your will get variances for many reasons e.g changing order sizes. Changes in raw material prices are not really production's concern - that is for purchasing to manage. Production are concerned about using the right material in the right quantity. If you uwe FIFO for materials then you will always get variances because your component costs are changing, but you are not always cost rolling the BOM.
You have to consider variance between the Production order Estimate and the actual, as being in production's hands, but the variance between production actual raw material costs and the standard BOM cost to be passed to inventory is outside their control and is more down to purchasing.
A combination of Fifo and Standard does not make too much sense.
FIFO reflects actual costs, typically for items with rapidly changing prices. Whereas standard by definition assumes stable costs or it does not make any sense to have a standard.
If the variance from standard is small, as it should be, then its not a material difference and is covered by the GP margin. If its large, then use another method. You will get the odd bad purchase or bad production run and the odd high volume favourable purchase and long run with favorable costs. A standard only makes sense for a standard quantity. Variances help you understand those one-offs. Variances are not a problem, but an analysis tool.
If your philosophy for inventory valuation is standard, then that should also be the philosophy for cogs.
Your raw materials should either be standard or weighted average ( under ifrs they should be within 3% of each other- both expect relatively stable costs. The difference is more about whether sales and operations should be managed separately or whether gains and losses are passed on above the line Standard is effectively an expected mean average.).
