  Ballistic graphene samples in a multimode regime show the sub-Sharvin charge
transport, characterized by the conductance reduced by a factor of $\pi/4$
comparing to standard Sharvin contacts in two-dimensional electron gas, and the
shot-noise power enhanced up to $F\approx{}1/8$ (with $F$ the Fano factor)
[Phys. Rev. B 104, 165413 (2021)]. Here we consider the disk-shaped (Corbino)
setup in graphene, with inner radius $r_1$ and outer radius $r_2$, finding that
the multimode conductance is slightly enhanced for any $r_1<r_2$, reaching
$(4\!-\!\pi)\approx{}0.8684$ of the Sharvin value for $r_1\ll{}r_2$. At the
same limit, the Fano factor is reduced, approaching
$(9\pi-28)/(12-3\pi)\approx{}0.1065<1/8$. Closed-form approximating expressions
for any $r_1/r_2$ ratio are derived supposing incoherent scattering of Dirac
fermions on asymmetric double barrier and compared with exact numerical results
following from the mode-matching method. Sub-Sharvin values are restored in the
narrow-disk limit $r_1/r_2\rightarrow{}1$. For experimentally-accessible radii
ratios $0.5\leqslant{}r_1/r_2\leqslant{}0.8$ both the conductance and the Fano
factor are noticeably closer to the values predicted for the $r_1\ll{}r_2$
limit, yet still differ from standard Sharvin transport characteristics. The
system behavior upon tuning the electrostatic potential barrier from a
rectangular to parabolic shape is studied numerically, and the crossover from
the sub-Sharvin to standard Sharvin transport regime is demonstrated.
Implications for a finite section of the disk are also discussed.
