You have two different situations in the examples that you mention. The first is both models starting in base to base contact. So active model declares
CC using MA3. The model in base contact can only declare
CC or dodge which would be resolved after the
MA attack. Any models with
LOF would declare their
AROs before the
MA attack is resolved so they would still be shooting into a combat with a friendly model regardless of the outcome of the
MA attack. So they would be shooting into combat with a -6 modifier.
The second situation is an impersonator moving into base contact and then attacking using MA3 with its second short skill. Again the model in base contact can only
ARO with
CC or dodge as the impersonator isn't revealed until its in base contact with the model. Models with
LOF would still only be able to
ARO at the point where the model is revealed, so once it gets into base contact, at which point its in
CC with a friendly model. So again any
AROs after the model is revealed would be shooting into combat with the -6 modifier.
Heres a link to an example of
AROs against camo models moving into base contact but it would apply equally to impersonators.
http://infinitythegame.wikispot.org/Camouflage_Example