On my paper brokerage account, I can see that this appears to not hold true ...
Daily P&L Financial Instrument Position Last Market Value Prior Close Change (Last - Prior Close)
310 SPY 100 372.1 37,210 369 3.1
178 SPY Dec30'20 369 CALL 1 3.84 383 2.05 1.79
158 SPY Dec30'20 369 PUT -1 0.63 -63 2.21 -1.58
-310 SPY CFD -100 372.1 -37,210 369 3.1
336 Sum of Options portofolio 3.21 320 -0.16 3.37
The SPY and SPY CFD positions do indeed move together; however it seems that my options portfolio supposed to simulate SPY has made 336 today instead of 310.
What is going on? Does it have to do with the spread / fact that it's a paper portfolio? Or is the synthetic only guaranteed to have the same value as the underlying at expiry ... ? Would it have to do with the change in volatility, as VIX is down today ~0.5%? Or something else?