I find that XP gains after 50 are already slow enough. My current character is level 65 after playing entirely too long into a Nexerelin game. I doubt even the most hardcore of grinders could top 80.
Why don't you test the number extremely low or extremely high to see if it works? Try 0.01 and 100. One of them should earn you 10+ levels off your first battle, the other won't even budge the meter, if it works.
I tested it out, and yeah, I reduces it significantly. The thing is, last game with Nexerelin i reached level 90 in almost no time. I picked a world in a system with many other worlds/traders- the bigger the better. Then i broke the station, raided it until the people living there begged me to Saturation bomb them already. Then i just gave it to a faction i liked. THEN i sold all the materials i raided off of' em right back to the planet. And oh boy they want A LOT and pay A LOT for about anything. Then i go to any nearby world, buy everything i can and just go to the *** world to sell. I get millions of exp just from "profitable trade". It's really broken and cheesy and that's why i need to nerf exp gain.