PortableApps.comInstaller.nsi
Line 1065:
Output of ${DriveFreeSpaceCustom} $3 is in MB. It should be converted to KB because output of ${GetSize} $4 is in KB.
Otherwise all calculation in Lines 1070 to 1088 are all wrong.
Similar calculations in Line 594 and 950 are correct.
This has been fixed in 3.8.15 along with some refinements. Thanks for the heads up!
Sometimes, the impossible can become possible, if you're awesome!