When taustar is large, u0 is consistently found to be ~0.5, even for high u0 values. From the contour plots, we see that the parameters are much less constrained for taustar=3 than for taustar=1.
Infinite resolution models for taustar=3
taustar=3; u0=(0.9:0.5); continuum
taustar=3; u0=(0.9:0.5)
taustar=1; u0=(0.9:0.5)
(3, 0.9)
taustar=2.60 +/- (2.35:2.89)
u0=0.990 +/- (0.797:0.990)
norm=2.15e-4 +/- (2.03e-4:2.25e-4)

rejection probability = 7%
(C=215.33; N=274)
(3, 0.9)
taustar=3.47 +/- (2.70:4.36)
u0=0.527 +/- (0.442:0.691)
norm=1.94e-4 +/- (1.84e-4:2.04e-4)

rejection probability = 32%
(C=205.14; N=274)
(1, 0.9)
taustar=0.974 +/- (0.831:1.18)
u0=0.909 +/- (0.878:0.958)
norm=1.99e-4 +/- (1.89e-4:2.09e-4)

rejection probability = 35%
(C=156.45; N=274)
(3, 0.8)
taustar=2.03 +/- (1.54:2.54)
u0=0.568 +/- (0.507:0.640)
norm=2.14e-4 +/- (2.03e-4:2.25e-4)

rejection probability = 24%
(C=228.29; N=274)
(3, 0.8)
taustar=2.23 +/- (1.71:2.89)
u0=0.471 +/- (0.413:0.554)
norm=2.17e-4 +/- (2.06e-4:2.27e-4)

rejection probability = 33%
(C=191.09; N=274)
(1, 0.8)
taustar=1.50 +/- (1.41:1.60)
u0=0.990 +/- (0.878:0.990)
norm=1.95e-4 +/- (1.85e-4:2.05e-4)

rejection probability = 8%
(C=151.78; N=274)
(3, 0.7)
taustar=2.92 +/- (2.36:3.44)
u0=0.710 +/- (0.586:0.990)
norm=2.13e-4 +/- (2.02e-4:2.24e-4)

rejection probability = 3%
(C=215.04; N=274)
(3, 0.7)
taustar=2.77 +/- (2.19:3.35)
u0=0.629 +/- (0.535:0.773)
norm=1.90e-4 +/- (1.81e-4:2.01e-4)

rejection probability = 24%
(C=180.63; N=274)
(1, 0.7)
taustar=1.06 +/- (0.815:1.31)
u0=0.675 +/- (0.627:0.715)
norm=2.00e-4 +/- (1.90e-4:2.11e-4)

rejection probability = 38%
(C=181.67; N=274)
(3, 0.6)
taustar=2.69 +/- (2.21:3.17)
u0=0.709 +/- (0.606:0.868)
norm=1.99e-4 +/- (1.89e-4:2.10e-4)

rejection probability = 87%
(C=253.61; N=274)
(3, 0.6)
taustar=3.30 +/- (2.68:4.03)
u0=0.547 +/- (0.473:0.665)
norm=2.18e-4 +/- (2.07e-4:2.29e-4)

rejection probability = 28%
(C=201.60; N=274)
(1, 0.6)
taustar=1.23 +/- (0.957:1.68)
u0=0.615 +/- (0.581:0.677)
norm=2.03e-4 +/- (1.92e-4:2.13e-4)

rejection probability = 45%
(C=184.58; N=274)
(3, 0.5)
taustar=3.37 +/- (2.43:4.89)
u0=0.436 +/- (0.355:0.990)
norm=1.97e-4 +/- (1.86e-4:2.08e-4)

rejection probability = 79%
(C=253.04; N=274)
(3, 0.5)
taustar=4.19 +/- (3.21:5.36)
u0=0.524 +/- (0.402:0.990)
norm=1.91e-4 +/- (1.81e-4:2.01e-4)

rejection probability = 8%
(C=176.50; N=274)
(1, 0.5)
taustar=0.809 +/- (0.558:1.12)
u0=0.486 +/- (0.445:0.524)
norm=2.04e-4 +/- (1.94e-4:2.14e-4)

rejection probability = 35%
(C=192.67; N=274)
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