=== Rotation-curve toy v4 summary (exp disk) ===
Rmax=30.0, n=1200, Rd=4.0, tail=[0.6Rmax..0.9Rmax]
     L   slope_mean    slope_std    Ntail         vmax         gmax
----------------------------------------------------------------------
   2.0       -1.975        0.250      360    1.052e+00    2.511e-01
   5.0       -1.199        0.116      360    1.930e+00    5.795e-01
  10.0       -0.419        0.048      360    2.651e+00    8.476e-01
  20.0       -0.076        0.015      360    3.311e+00    1.049e+00
  30.0       -0.001        0.018      360    3.601e+00    1.119e+00
----------------------------------------------------------------------
Interpretation: slope_mean ~ 0 => flat tail; ~ -0.5 => Newton-like decline.