I agree that a tether should not encumber your work on the boat. I have experimented with a variety of ways of attaching the jackline:
1 - along the cabin top, inside the shrouds, which meet the side decks fairly close to the cabin top. This keeps me comparatively inboard but more often than not, the carabiner on the jackline end of the tether snags something, especially often getting wedged in between the cabin top and a shroud. However if I do go over I might not necessarily end up with my face in the water.
2 - along the side decks, outside the shrouds. This is pretty good but means I have to make use of the very narrow side-decks on my boat to move around. In fact, this is normally a very comfortable way to go forward, but with a slippery sloping deck in rough weather it's obviously an added danger. It also means that if I want to unclip and clip to something else I have to lean over the side decks, bringing my weight too far outboard for safety. And of course lastly it means that if I go over, I'm definitely in the water.
3 - Single jackline, one end tied to each bow cleat, and looping abaft the mast with a good amount of slack. Tried this recently during a two-day singlehanded race, and really liked it. I could go from one side of the boat to the other without unclipping. I could stay clipped on in the cockpit and reach most of the things I needed to. The thing I haven't figured out yet is how tight the loop should be. Too tight and prevents me from working in the cockpit without unclipping, and might be hard to reach from the cockpit to (un)cilp. Too loose and it tends to drag around and might not keep me on the boat.
I think what I'd like to try next is the same as (3) but without much slack, plus a tether permanently clipped to something else that gives me access to the cockpit. Put on the new tether before taking the old one off to switch from cockpit to deck or back.
s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27