IUKP etf

[SheikYaManii]

calculating 5 year total return from Morningstar figures for iShares etf IUKP I get 26.29% , ishares website gives a similar 27% .
The theaic web page for uk commercial property ITs excluding healthcare gives 5 year average total return as 27%.
Average 10 year total return for Investment Trust Commercial Property is 36.7%, 10 year total return for IUKP etf is 128.74% so why the big difference over 10 years?