  Recent observations suggest the incidence of strong intervening MgII
absorption systems along the line-of-sight to gamma ray burst (GRB) afterglows
is significantly higher than expected from analogous quasar sightlines. One
possible explanation is a geometric effect, arising because MgII absorbers only
partially cover the quasar continuum regions, in which case MgII absorbers must
be considerably smaller than previous estimates. We investigate the production
of abnormal absorption profiles by partial coverage and conclude that the lack
of any known anomalous profiles in observed systems, whilst constraining,
cannot on its own rule out patchy MgII absorbers.
  In a separate test, we look for differences in the distribution function of
MgII equivalent widths over quasar continuum regions and CIII] emission lines.
We show that these anomalies should be observable in any scenario where MgII
absorbers are very small, but they are not present in the data. We conclude
that models invoking small MgII cloudlets to explain the excess of absorbers
seen towards GRBs are ruled out.
