For a 125 percent increase (120 dpi) you will need a 40x40 icon (= 32x32 * 125%)
If you don't have one, Inno Setup is likely to use the 32x32 scaled icon.
Your application seems to be using a different strategy, possibly zooming out 48x48.
Not sure why you should have a problem with scaling by 150% (144 DPI), since you have a 48x48 icon (= 32x32 * 150%).
I tested your icon in a simple installer, and in fact it shows a good icon at 150% zoom (tested on Windows 7 7).
In my installer, I have a .ico file with the following sizes: 16, 20, 24, 32, 40, 48, 60, 64.
It perfectly covers all needs with up to 200% scalability (192 DPI).
In addition, it is possible that there is a difference between the Ansi and Unicode versions of Inno Setup. They are based on different versions of Delphi, possibly using different strategies to select an icon. This may explain why you have problems with a 150% increase, while I do not.
I am using a Unicode version based on over a ten-year-old version of Delphi (Delphi 2009 vs. Delphi 2 since 1996).
Martin Prikryl Dec 17 '15 at 20:32 2015-12-17 20:32
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