Hi Emad,
It depends on your Icon file i.e. if it has multiples sizes/formats available the appropriate size will be utilized. If not the available image is displayed as is and not scaled. May be better to use an Icon editor and split the multi-format icon into individual single-format files. Also, another problem is that the Windows designer is 16-bit which renders the icon differently as compared to the compiled EXE which is 32-bit.
Regards