The following downloadable works are by Imam Muhammad Hashim al-Sindi with some replies to Shaykh Muhammad Hayat al-Sindi (who advocated placing on the chest). The file was sent to me from Shaykh Abul Hasan who has probably the most detailed evidences and discussion on this issue in his possession today. Wallahu a'lam.

http://www.4shared.com/file/83422459...him_Sindi.html

Wassalam