I have a large padeye low on the bridgedeck bulkhead, just below the companionway. With my long tether I can reach any part of the cockpit and go down the companionway but not fall out of the cockpit. Like jssailem, I have two folding padeyes, but mine are on the cabin top just to either side of the companionway. While clipped into and sitting in the cockpit, I can clip onto the jack lines with my short tether and then unclip from the cockpit. My short tether combined with the near center jack lines won't let me go over the side.
I should have put the folding padeyes further back on the bulkhead behind the cabintop. While I can sit and switch tethers, it is still a reach because the buckle/loop on the jack line causes me to reach a few inches further than planned. Another problem I have not yet solved is that my Jack lines interfere with my canvas dodger, I can't use them both at the same time. I don't normally use the dodger while sailing, but sometimes it would be nice.