I believe rogue poisons are currently bugged. Higher tier poisons are currently doing the same amount of damage as lower tier poisons. I performed an experiment recently where I crafted the tier I contact poison (
http://wiki.project1999.com/Asp_Poison) and the tier III contact poison (Visionistic Pain) and tested them against identical low level mobs. Both hit for the same amount of damage, 121, at level 30. According to the wiki
http://wiki.project1999.com/Skill_Make_Poison the tier III poison should have significantly higher scaling per level.
For further verification, I crafted a tier IV muscle lock snare poison (Spirit of Sloth) and poisoned a mob, allowing the poison to run its course. When it wore off, I received the message "Your muscle lock I has worn off."
It seems all higher level poisons are being treated as lowest level poisons.