Is there a way to adjust the particle collision threshold point ?

I've been searching for more than an hour now, and still haven't found what I'm looking for. I hope it's just not a matter of "search terms" that blocks the results... anyway!

Here's my problem. I've made a Shuriken particle snow storm and for a better result of the snowpowder effect, I'm using big foggy particles. I've set every collision particle properties to "Everything" and "World", and the "Lifeloss" value to 1. But still, my particle intersect with the vehicules and the storm is suddenly in the cars!

I assume the point of collision is on the particle center. But is there a way to make the collision functionnal on the whole particle surface ?

Thanks for your time!