Two recent papers quantified the real usage bias for the
real output in a ring being the true one, and shows that
the current biasing is much too weak.
While we wait for a better solution, we increase the ratio
of recent-to-total fake outputs, as well as decrease the
time window for recent outputs, so that half the fake outs
are selected within the last 1.8 day. Value plucked from
figure 10, page 11 of An Empirical Analysis of Linkability
in the Monero Blockchain, 2017, Miller et al.
This is also arbitrary, of course, but serves as a stopgap
till a better selection algorithm is chosen.
ac1aba90f8