How to distinguish between left and right motors in joystick forcefeedback effects

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C#

DirectX

//using Microsoft.DirectX
//using Microsoft.DirectX.DirectInput
DeviceList dList = Manager.GetDevices(DeviceClass.GameControl, EnumDevicesFlags.AttachedOnly);
DeviceInstance dInstance;
foreach (DeviceInstance deviceInstance in dList)
{

dInstance = deviceInstance;
break;
}
//Initializing Device "12btns / 2anlg vibration Joystick "
EffectObject eo = null;
Effect eff = new Effect();
Device dev = new Device(dInstance.InstanceGuid);
dev.SetCooperativeLevel(this, CooperativeLevelFlags.Exclusive | CooperativeLevelFlags.Background);
int[] axis = new int[0];
foreach (DeviceObjectInstance devoi in dev.Objects)
{
if((devoi.Flags & (int)ObjectInstanceFlags.Force) != 0)
{
axis = new int[axis.Length + 1];
axis[axis.Length - 1] = devoi.Offset;
}
}

dev.Acquire();


eff.SetDirection(new int[axis.Length]);
//int the next step when trying "new int[axis.Lenght]" causes
//"Value does not fall within the expected range" error
//maybe its a bug in DirectX Inner Constructor Code.
//Directx.Dll Version :5.04.00.2904 - DirectInput.Dll version 9.15.779.0000
eff.SetAxes(new int[1]);

//other properties.
eff.TriggerButton = (int)Button.NoTrigger;
eff.Duration = 25000;
eff.Gain = 10000;
eff.Flags = EffectFlags.Spherical | EffectFlags.ObjectOffsets;
eff.Duration = int.MaxValue;
eff.SamplePeriod = 0;


eff.TriggerRepeatInterval = (int)DI.Infinite;
eff.UsesEnvelope = true;
eff.EffectType = EffectType.ConstantForce;
eff.StartDelay = 0;
eff.Constant.Magnitude = 10000;



//Guid For Constant Force Effect From Registry :HKLM\CurrentControlSet\Control\MediaProperties\PrivateProperties\Joystick\OEM\VID_0079&PID_0006\...
eo = new EffectObject(new Guid("{13541C20-8E33-11D0-9AD0-00A0C9A06E35}"),eff,dev);

//starting Effect (1 iteration)
//both Motors.
eo.Start(1);

//now I need to send Force Effect to specified Motor(distinguish between left & right);
// like the one in GameControllers.ControlPanel.Vibration Test
//exemple : [RightForce|leftForce|BothForce]
//changing [SetAxes|SetDirection] Parameters Below Didn't work;
//neither editing registry Values for OEM
// ForceFeedBack effects didn't work too;

What I have tried:

hanging [SetAxes|SetDirection] Parameters
editing registry Values for OEM ForceFeedBack effects
Nothing Worked at all