It's not necessarily an and/or. When thinking about FC and VC you should also be thinking about the value chain.
For example:Raw Mats (VC) and R&D (FC) are at the beginning of the chain. Labour (FC or VC), electricity (VC), and rent (Generally FC) are in the middle (production/manufacturing). Transport/shipping/delivery (can be FC or VC) is at the end.
That being said, if you clearly have an operational prompt (i.e. we're seeing bottlenecks that have cause an increae in our costs), then go value-chain. Likewise, if you hear "We've seen costs rising over the past 3 years", and you can generally go FC/VC. However, if you get the same question and you're a vertically integrated company (perhaps Oil&Gas), you may want to talk about both simultaneously (keep it structured though).