Magnetic reconnection X-lines have been observed to be more common
duskward of midnight. Thin current sheets have also been postulated to
be a necessary precondition for reconnection onset. We take advantage of
the MMS tetrahedral formation during the 2017--2020 MMS tail seasons to
calculate the thickness of the cross-tail neutral sheet relative to ion
gyroradius. While a similar technique was applied to Cluster data,
current sheet thickness over a broader range of radial distances has not
been robustly explored before this study. We compare this to recent
theories regarding mechanisms of tail current sheet thinning and to
recent simulations. We find MMS spent more than twice as long in
ion-scale thin current sheets in the pre-midnight sector than
post-midnight, despite nearly even plasma sheet dwell time. The
dawn-dusk asymmetry in the distribution of Ion Diffusion Regions, as
previously reported in relation to regions of thin current sheets, is
also analyzed.