Beware waking them up !
I will probably just leave it blank until they tell me to check a box.[/QUOTE]
I think it is a very bad idea to leave it blank - put a middle unsuspicious amount ! Main receipt for happiness in Thailand is "low profile" and "no confrontation" - when I have to hit hard here I do it with a lawyer - and can win even against "untouchables".
The immigration process is so smooth in BKK because the officials at the desk are strictly trained and limited on their task (some even smile) - almost "analphabets" concerning their English skills. I prefer however NOT having to deal with a supervisor - they must have such guys - and they may even be decently proficient in English.....