Need help with scale of 3D model

I am new to three.js.
I use the gridhelper to draw a grid then I load a gltf model into this grid.
I add drag controls and I can drag my model. So far so good.
Trouble is when I move the model it stays at the same scale.
What I want to do is create the ‘illusion of depth’ that is, when I drag my model towards the ‘end of the grid’ down the back my model will become smaller and smaller.
Can you help?

What type of camera are you using? Consider to share your app as a live example or as a github repository.

I am using PerspectiveCamera

I already tried to change these values but that did not give me the desired result.

Any chances to share your code as a live example ( Sharing a github repository is also a good idea.

My app is using Meteor.js. Here is the code though you will not see the output:

I think you are going to need to edit DragControls - see this:

instead of _camera.getWorldDirection( _plane.normal ) you want your grid normal

Thank you for your help.
I think TransformControls will do the trick.