Is it not easier if you do it like this:
$myPath = exo_getglobalvariable('HEPubStorageLocation', '');
$configPath = '/CONFIG/config.ini') // CONFIG is a Subfolder
$configFile = $myPath.$configPath;
/*
e.g.:
yourexe.exe
|- CONFIG DIR
|-- config.ini
*/
if(file_exists($configFile) {
echo...