For certain marks if you are a gatherer depending on the distance from you to the party you will not get credit. This happened to me twice yesterday when I was out gathering in the southern most region of the map and the party was hunting a rank V monster far to the north. Otherwise even if I am in range I will just pass on the gear since I did not contribute.

I think the credit needs to be based off of party damage + individual damage. Meaning you have to hit the enemy at least once or twice to get full credit. Otherwise if that is not possible shorten the credit range to 300 or less yalms. That would shorten the range enough for leechers to not have access to each and every drop. Right now I think the range is about 750 yalms or more to get credit.