As a linguistics major and a Japanese speaker for 6+ years, the positioning shown on the article looks pretty correct to me (maybe off by a tiny bit). Try making the English 'l' and 'r' sound, and you'll find that the Japanese 'r' will fall in between those two (in regards to tongue position).
http://upload.wikimedia.org/wikipedi...ticulation.svg
The tongue position lands in between 4 and 5, the area called the alveolar ridge. That's where the Japanese 'r' sound is made.