Not sorting correctly Magento 1.9.1

[mariospas]

I am using sort by Best Sellers as default for the below category. I set up 3 days as the calculation history.
But I noticed that best seller has exactly the same sort as item-position
BEST SELLER SORT
https://www.iqshoes.gr/women/categories?___from_store=en2&___store=eng1&dir=asc&order=bestseller

ITEM-POSITION SORT (manual sorting by giving position numbers)
https://www.iqshoes.gr/women/categories?___from_store=en2&___store=eng1&dir=asc&order=item_position

What can I do ? Should I remove all the positions from my items and give them 0 ?