The % is the change in price for each symbol from the close to the open. In the case of IWM, I show an adjusted open also where I added in .38 for the dividend. With the adjusted numbers the % are close enough and are not out of line for an open with such a small gain/loss.
Below are the actual closing numbers for y and today. I added .38 to today's IWM number. %'s are close enough to 2:1 for the normal daily error that I see.
Cls Cls % chg
IWM 76.28 76.58 0.39%
UWM 36.71 37.04 0.90%