SPX is usually around 10x that of SPY. SPY is at 217 means SPX is roughly 2165 to 2175. I understand that one is an ETF and the other just 'tracks', SPY gives out dividends, SPY is more liquid, etc.
However, for example, for Sept 2 expiry the call premiums are as follows (both of these are PM settled):
Call SPY @218 = $0.59 Call SPX @2180 = $4.1
I would have expected SPX to be around >= $5.5 Can any experienced traders explain the discrepancy?