I just changed oar towers, and was contemplating moving around my oar stops. That led me to google, and eventually the magic words that talk about oars.
Rafters seem to be very small beer in the wider rowing scheme of things, so this should be taken with the understanding it's for boats other than 14' SB rafts. Still I found it useful. This a topic here periodically, but a search here didn't turn up the reference I found.
The reported optimal location of the 'button' (non-rafter word for oar stop) is 7/25 from the top for the total oar length. YMMV.
I make no judgement on that, other than screwing around with mine for a couple of years put me close.
NRS says 1/3, FWIW.
Link to reference is