I've crossed from Malaysia to the Middle East many many times and I'd say that I've had better success getting hold of Chennai over the Bay of Bengal, but not so much success with Mumbai over the Indian Ocean.
I'd say that about 10% - 20% or so of the time we've gone all the way from talking to Mumbai on VHF all the way to Muscat (and the reverse) without being able to contact Mumbai on any HF frequency once.
Quite often only one frequency will be working and the ATC bloke will be flat-out on it ..... you won't get a word in edgeways and will have to wait until they SELCAL you, and even then it may not work.