  The assessment of the frequency of planetary systems reproducing the Solar
System's architecture is still an open problem. Detailed study of multiplicity
and architecture is generally hampered by limitations in quality, temporal
extension and observing strategy, causing difficulties in detecting low-mass
inner planets in the presence of outer giant planetary bodies.
  We present the results of high-cadence and high-precision HARPS observations
on 20 solar-type stars known to host a single long-period giant planet in order
to search for additional inner companions and estimate the occurence rate $f_p$
of scaled Solar System analogs, i.e. systems featuring lower-mass inner planets
in the presence of long-period giant planets.
  We carry out combined fits of our HARPS data with literature radial
velocities using differential evolution MCMC to refine the literature orbital
solutions and search for additional inner planets. We then derive the survey
detection limits to provide preliminary estimates of $f_p$.
  We generally find better constrained orbital parameters for the known planets
than those found in the literature. While no additional inner planet is
detected, we find evidence for previously unreported long-period massive
companions in systems HD 50499 and HD 73267. We finally estimate the frequency
of inner low mass (10-30 M$_\oplus$) planets in the presence of outer giant
planets as $f_p<9.84\%$ for P<150 days.
  Our preliminary estimate of $f_p$ is significantly lower than the values
found in the literature; the lack of inner candidate planets found in our
sample can also be seen as evidence corroborating the inward migration
formation model for super-Earths and mini-Neptunes. Our results also underline
the need for high-cadence and high-precision follow-up observations as the key
to precisely determine the occurence of Solar System analogs.
