Omission Filter

anyone worked them out yet?

[JonnyWales]

Always featured highly until the last Google update. Site is a PR5 and "currently" ranks as follows with last months position in parenthesis:-

KEYWORD1 - position 42 (55)
KEYWORD1 KEYWORD2 - NOT SHOWN (11)
KEYWORD1 KEYWORD2 KEYWORD3 - position 20 (1)

Unfortunately most traffic (90%+) comes from the KEYWORD1 KEYWORD2 combination. I'm assuming that some sort of filter in the algo is removing me from the SERPS for that search term. I had thought it was perhaps to do with density which score 10%, 24% and 27% respectively but some sites still appearing have much greater densities.

Is there any point doing anything now or should I just wait until the next update? If I did make any changes is it likely to effect my position or is everything now pretty much stable until the next update?