Appears you guys are right. I was thinking the new system merely set a maximum bid. Clearly as a couple of you pointed out I was wrong.
Apparently when the Japanese team posts a player they have to guess what teams might be willing to pay and then announce a specific "release fee" amount. Any team can negotiate with the player and the team who signs him pays the "release fee".
http://mlb.mlb.com/news/article/mlb/mlb-nippon-professional-baseball-agree-on-revised-posting-system?ymd=20131216&content_id=66016648&vkey=news_mlbThat is fine for Tanaka. Several teams will be in at the $20 mil fee. But what of lesser players?
For example in 2011 Norichika Aoki was posted and winning bid was $5.329 mil. This new system has the potential to be a mess in future years. It definitely puts a burden on the Japanese team to get it right on estimating how much a player is worth. Value him too high and kill intereste. Too low and leave money on the table.