Scaling Rendered Object To Cover the Found Image Target On Screen

Hi, We are trying to render an object (a toy car which is a little bit bigger than a book) on a target image on runtime. We are creating and spawning the object with "onTargetImageFound". The problem is our rendered object is too small. We need to scale the object (which we will create when target image is found), for example, same size as the found Image Target on our camera and project it, we tried giving it a static scale however the object is not resizing (naturally) when we move the camera further from the object. Is there any way to get the scale of the ImageTarget? There are two attached images one (with a tiny white point) is the original one without applying anything, second one is scaled by us with random numbers (45,10,45). Btw the object(prefab) we try to spawn is not small normally when we drag it on the scene. Thanks in advance.