Of course entities are rendered smaller when you increase the isometric view volume, everything would be highly confusing and impractical (I suggest you google isometric and perspective rendering).

I assume you want to create some kind of radar functionality (and don't want to use 2D objects like panels or draw_...)? What you could do is fill the entity's scale_x vector (let's say with a view.right/256.0 formula) or do the scaling in a vertex shader which would be notably faster when you have to scale often/ every frame.