Force PS Jobs to run all steps on the same server

We have two App Servers (PSUNX and PSUNX2) and several PS Jobs where the Server Name field was set to PSUNX. These jobs were set this way to ensure all steps run on the same App Server, which is required when a step gets a file and places it on the server and the file is used again in a subsequent step. We would like to clear the Server Name field so these jobs can run on either PSUNX or PSUNX2, especially when PSUNX is down.

We reviewed our process scheduler data and found that several jobs (which don't have a server name defined) have been starting on one server and switching to the other. (Example: PS Job with 2 App Engine programs - AE 1 ran on PSUNX and AE 2 ran on PSUNX2).