Hi Joe,
The way we render backdrops in Chief is tied to the positioning of the camera and not related to the location of the model in the plan. Having your model near the origin or really far away won't impact how the backdrop looks behind it. Moving around the camera relative to the model will change the centering of the backdrop and zooming the camera in or out will change the scale of the backdrop in relation to the model.
One tool which is helpful for positioning the background in your plan is the "Rotate Spherical Backdrop" tool, which can be found in the same tool palette as the "Cross Section Slider" (see attached image). This tool allows you to drag across the screen and adjust the horizontal rotation of your backdrop to get it to line up as desired.
In terms of changing the perspective of the backdrop and maintaining an image that looks accurate, we don't have a way to do that in Chief as the perspective of a spherical backdrop is a result of the original image it comes from and where the camera was positioned within the environment when it took the picture(s) used for the backdrop. Yes, you can change the horizontal tile size to 2 to make the backdrop appear further away, as Steven mentioned, but doing so results in mapping a spherical image onto a hemisphere so it won't look completely correct.
