  A long standing problem in the study of Active Galactic Nuclei (AGNs) is that
the observed VLBI core is in fact a blending of the actual AGN core
(classically defined by the $\tau=1$ surface) and the upstream regions of the
jet or optically thin emitting region flows. This blending may cause some
biases towards the observables of the core, such as its flux density, size or
brightness temperature, which may lead to misleading interpretation of the
derived quantities and physics. We study the effects of such blending under the
view of the Korean VLBI Network (KVN) for a sample of AGNs at 43 GHz by
comparing their observed properties with observations with the Very Large
Baseline Array (VLBA). Our results suggest that the observed core sizes are a
factor $\sim11$ larger than these of VLBA, which is similar to the factor
expected by considering the different resolutions of the two facilities. We
suggest the use of this factor to consider blending effects in KVN
measurements. Other parameters, such as flux density or brightness temperature,
seem to possess a more complicated dependence.
