I don't agree with andrew because they are some surely speak above words with light tone.It is not important for above word because it is just 語法化輕聲。We should be more concern about light tone in nouns which have completely different meaning.做人 has two meanings,most people don't know it means marry.
死si2 drop from 5 to 3 or 2 in xia/chiang but chuan don't drop,we have 55 in Anxi sect or 54 in others.We are not talking about sandhi . You can check this sound like 拍死 in xiamen news。