Question Spawning a Gameobject with correct position after pose estimation from CPU Image using ARFoundation

I am working on an algorithm which estimates the 6d pose of an object by providing the CPU image ( using
TryAcquireLatestCpuImage) and the camera intrinsics (TryGetIntrinsics). When i project the object cad with the estimated position and rotation using the same intrinsics I get good results using opengl. But when i spawn the object 3d model in unity using ARFoundation the z position shows an offset. I realized that although arcamerabackground script imposes a projection matriix which is same as when calculating the pose estimates but the image size is changed (the cpu image is 640X480 but in an ARSession the image size is the screen size (2340X1080 on my android device)) of the device due to which the fov changes and I can observe the projection offset. How to take care of the change in fov so that my projection fits.