Generally ad selection for all positions in Yandex direct depends on CTR and a price. The best ads are shown in top left corner of search results. There are 3 positions. The position of the ad decreases with the price per click.The rest of the ads are shown in top right column.
(source:http://direct.yandex.ru/)

From 26.07.07. Yandex Direct has made a minimum price for a keyword, dependent on how effective is your campaign. This will allow to increase search quality for the user. It will also give an advantage against the competition, for the most relevant, most effective ( most interesting for the user) ads.
For this purpose, Yandex has created a new parameter which depends on the history, which changes in a real time with the process of campaign working. Based on CTR, Impressions, amount of days of working campaign.
Minimum price ,shown in the campaign setting interface, is the price for which the impressions in Yandex search results are possible.If the campaign becomes less effective, price per click will increase, however when quality is improved, the price drops back up to 0.30 Rubles.
(source:http://help.yandex.ru/direct/?id=992580)