I have been editing the duels (adding in a blank space and saving etc) every day or two to try and keep them orange boxed for everyone. Not sure if it works, but the latest has 25 votes so far and several hundred views, as you say this may be repeat views.
The painting competitions were always supposed to be "the main show" really so if there is a bias one was or another I'm glad it is to them. Hopefully the duels provide what they were designed for, a casual, fun format to challenge yourselves and each other and provide more great works for others to view.
Websites often work on a 10%-20% rule, 15-20% active, 15-20% of those are likely to votes/register for events/take part, etc etc. so to get 50 active members and then 20-30 votes from those means we are above average guys so don' worry too much!
To be honest I haven' been voting on duels as I host them all, but I'll start if you like, adds one more to the count!