  We study the fine tuning associated to a `Natural Supersymmetry' spectrum
with stops, after RG running, significantly lighter than the first two
generation sfermions and the gluino. In particular, we emphasise that this
tuning should be measured with respect to the parameters taken to be
independent at the assumed UV boundary of the renormalisation group flow, and
improve the accuracy of previous approximate expressions. It is found that, if
running begins at $10^{16}~\rm{GeV}$ $\left(10^5~\rm{GeV}\right)$, decreasing
the UV stop mass below $0.75$ $\left(0.4\right)$ of the weak scale Majorana
gluino mass does not improve the overall fine tuning of the theory. In
contrast, it is possible to raise the first two generation sfermion masses out
of LHC reach without introducing additional tuning. After running, regions of
parameter space favoured by naturalness and consistent with LHC bounds
typically have IR stop masses of order 1.5 TeV (0.75 TeV), and fine tuning of
at least 400 (50) for high (low) scale mediation. We also study the fine tuning
of theories with Dirac gluinos. These allow for substantial separation of the
gluino and sfermion masses and, regardless of the scale of mediation, lead to
relatively low fine tuning of order 50. Hence viable models can still favour
light stops, but this requires extra structure beyond the MSSM field content.
