At 1/3rd, you have a pretty low bearing rate so it will take longer to build a solution. You have to keep a watch for the contact's ability to hear you in the signatures screen. If their sensors are below 10 dB, you can go faster and they won't pick you up. It is possible there are airplanes or helos nearby that are seeing you.
To quote ramjb here, to be stealthy doesn't mean being slow:
|