the model file that has the citroends23_hi is considered "Very High" Lod file which is separate, maybe this is what GreenAid meant. In vehicles meta there are setting lines which can be set up how many meters the car model shows the "Very High" lod model before it goes into High and then from High to Medium etc.
I think what GreenAid meant is - your highest polygon count model should be Very High setup which you already have in citroends23_hi, then it should probably go into High which should be like 30-40k polies, then into medium which in your case is 8k polies and so forth.
The way you have it setup now is your Very High and High lods are the same. So it basically goes from Very High / High lods straight into Medium and the difference is noticeable.