No Captain OE - so always SIC.
I log for a three-person crew:
for a 9.6 hour flight
Flight time: 2/3*(9.6) = 6.4 hours SIC.
Also, in an unused column, the total time as: <9.6>,in angle brackets, just to record the total "time aloft" that included my sleep/rest time. The angle bracket-enclosed number does not figure in any totals. (It's already been tracked by the company, and in my little red book for weekly, monthly, and calendar limits, where does apply). If I was in either seat for a total of 3 hours or 8 hours, still log just this 2/3 fraction: 6.4)
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and a four person crew:
for a 9.6 hour flight
Flight time: 1/2*(9.6) = 4.8 hours SIC,
And the non-totalled <9.6> in angle brackets in my unused column...
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and of course, a two pilot crew:
for a 6.7 hour flight
I log 6.7 hours SIC