Subject: Re: OT: SPY vs SPX options and IV
Another interesting thing I saw just now.

S&P 500 INDEX (^SPX)
SPX Apr 2025 5700.000 call is Bid 241.80 Ask 243.10
Volume 200 Open Interest 2.67k

but
S&P 500 MINI SPX OPTIONS INDEX (^XSP)
XSP Apr 2025 570.000 call is Bid 17.52 Ask 18.34
Volume 1 Open Interest 10

XSP is 1/10th the size of SPX, so I expected the prices would also be 1/10th, but this is clearly not the case.
WHY??? They move in tandem, so why?

Each call of SPX is $24,200 while each call of XSP is $1,800.
Looking at the volumes & open interests, SPX is what the big players use and XSP is what us pipsqueaks use.

If you wanted SPX call, why wouldn't you buy 10 of the XSP call? $18,000 vs. $24,200. What am I missing?