Would there be someone lurking here who would have knowledge of Malaysian (and Vietnamese) primary radar coverage ? My understanding is that the typical maximum range of current civilian PSR is about 60 miles, question is where are the facilities located.
http://aip.dca.gov.my/aip%20pdf/ENR/...1.6/Enr1_6.pdf
A bit dated, but I don't think it'd change dramatically.