Pretty sure this question was asked and answered, fairly recently.

Unless it has  been bugged, which is possible, you might have just been unlucky, because I would say what you wrote just isn't factual.

I would suggest that because Ghosts have less variety of items dropping, the chance of VIP points is more likely than with invaders, so your observation could be an illusion.   

 Futher, I doubt that  what you think you have seen, is level dependant, but could be, an exception perhaps is Ubers, which I haven't attacked recently, but you did write invaders.

Even if was happening,it's not going to make a big dfference,as the amounts aren't enormous.

Here is the link to the post I mentioned earlier.

https://plarium.com/forum/en/vikings-war-of-clans/583_technical-support/609568_vip-points-not-showing-up---not-available-to-apply/