That is right. With premium program you can earn up to 5.10% (+1.02%)* annual interest.
The method to raise your interest from 4.08% is by investing in the FUN tokens? I am currently running my coins on the base interest of 4.08% and any boosted amount is always welcome. I thought the FUN token investment was a separate scheme altogether, meaning that two investment schemes were running on the site side by side - correct my if I was mistaken.
It is not a separate scheme altogether. From a certain tier in the premium membership you will start to get more interest. If you have at least 12.500 FUN tokens and hold them more than 360 days, than your interest gets boosted with +10%. If you have 500.000 FUN tokens (the maximum tier), you will get up to 25% extra (so 5.10% annual interest) after 1 year of holding the tokens.