Blur Effect issue ?

Hello there, i’m new to toon boom. I come from AE. I do compositing and i try to see what we can do in this soft.

I try to make a vignette like in this tuto :

So with a drawing and a blur effect.
but i’ve a problem when i render my scene.
I have a camera movement from sky to ground ( top to bottom ) and my vignette is jsut on the ground.
It seams like TBH render the effects only when they are visible by the camera, i mean when they enter the field of view. So it makes me my vignette to appear as if there was an animation on the transparency of it when the camera move is approching the ground.

Do i have to render a bigger image and go crop inside in AE to fix this ?

Any suggestions ?

It might be because of my way to make the blur i think. I did the blur directly in the matte blur used to change the color (because there is this option to add blur). It seems that when i live it to zero and i use a gaussian blur after there is not the problem.
is it possible ?

and without the radial blur it’s even better and faster. it was the repeat edge pixel ON in the gaussian blur that f*** my render…
Hope it can be usefull to someone…