  In the forward end-cap of the Belle II spectrometer, particle identification
is provided by a proximity focusing RICH detector with an aerogel radiator
(ARICH). The ARICH's primary function is to effectively distinguish between
pions and kaons in the momentum range of 0.5 GeV/c to about 4 GeV/c, as well as
to contribute to identification of low-momentum leptons. Since its operation
began, Belle II has collected over 420 fb-1 of data. Based on this large data
sample, studies of several effects that impact the performance of the ARICH
detector were carried out. In this paper, we present a comparison of the
observed Cherenkov ring image and detector particle identification performance
in the measured data and detector simulation. Furthermore, we highlight recent
efforts aimed at enhancing the ARICH's performance by taking into account the
effects of particle decay in flight and scattering in materials before the
detector, as well as by refining the probability density function used for
particle identification likelihood evaluation.
