Something i don't get with 3D

Hello there,

First of all im glad to now be officialy a member of the hitfilm community after buying the software 2 weeks ago !

Ive created a "magic circle" in 3D to put a character in a middle of it that will make him disappear, but when i import my video footage with the character, i can't have him in the middle of the circle, even if i select 3D for both layers.

The circle goes behind or in front of the character, what should i do to have him in the middle ?

Thanx in advance.