2014 June Q1 Cocoa

This is a question about calculating Contract number of exchange futures.

When we need to convert exposure currency to the same currency as contract size, I thought normally we use say ($1000/expire rate of exchange future)/contract size in CHF

But in this question, it actually calculate the expected rate on the date payment happen. I understand this and it makes sense.

I just don’t know when to just use the expiry rate and when to use predicted closing rate

Thanks