Android 6.0 - Cannot create directory on SD card

Question

I have a problem creating directory on SD card.
AndroidManifest.xml contains neccessary permissions:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

<application...

Also for Android 6.0 I ask these permissions at runtime:

int permissionCheck1 = ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE);
int permissionCheck2 = ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
if (permissionCheck1 != PackageManager.PERMISSION_GRANTED || permissionCheck2 != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this,
                new String[]{Manifest.permission.READ_EXTERNAL_STORAGE,
                        Manifest.permission.WRITE_EXTERNAL_STORAGE},
                REQUEST_READWRITE_STORAGE);
} else {
    init();
}

and waiting for results:

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    switch (requestCode) {
        case REQUEST_READWRITE_STORAGE:
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                init();
            } else {
                Toast toast = Toast.makeText(this, "Read / Write storage permissions required", Toast.LENGTH_SHORT);
                toast.show();
            }
            break;
        default:
            break;
    }
}

My application determines two available storages:
internal - /storage/emulated/0
and external (removable SD card) - /storage/6052-CD5B

I create folders using

new File(parentDirectory, newDirectoryName).mkdirs();

Results:
I can create folder inside /storage/emulated/0.
I can create folder inside /storage/6052-CD5B/Android/data/myapp (this is my application folder).
But I can't create folder in /storage/6052-CD5B outside my application folder, e.g. images folder /storage/6052-CD5B/DCIM.

It seems that granted permissions give me access only to application-specific folder. Is it so? If not, how can I finally get write access to other SD card folders?