It's possible that the level of the mission effects the standing gain - you'd have to calculate each of the gains from your transactions to see if they were what they should have been in order to find out, but if the mission level affects the standing I'm sure someone else would have noticed by now?
Ughmahedhurtz: You've trained the social skills to get improved standing and benefits right? Right?!
It's nothing like COH, completely different mechanism. You can get missions from any agent whose standing requirements you meet and standing requireemtns are listed in the agent's Show Info screen. The quality of an agent directly affects what rep is required to get missions from them. The following is a bit rough because it's cut and pasted from a spreadsheet but it should give you a clue:
Level/Quality/Requires Standing
1/-20/-1
1/-10/-0.5
1/0/0
1/10/0.5
2/-20/1
2/-10/1.5
2/0/2
2/10/2.5
3/-20/3
3/-10/3.5
3/0/4
3/10/4.5
4/-20/5
4/-10/5.5
4/0/6
4/10/6.5
5/-20/7
5/-10/7.5
5/0/8
5/10/8.5
5/20/9
So you can see that the lowest quality L3 agent requires only a standing of 3 to work with - although obviously not every corp has the full range of agents. To find one try here:
http://eve-agents.com/