It’s not just about stressing the “tori” part – any word with “hi” can have a more “hissing” sound. The level of “hiss” (for want of a better word) just depends on the speaker. Also, it largely depends on the kana coming after it: “hima” will generally have less hiss than “mannenhitsu” or “hikari”. Something to do with how /m/ is a bilabial consonant while /k/ and /t/ are plosives… or something.
If anyone knows what I’m talking about, could you back me up, maybe rephrase it so it’s a bit clearer? :D Or tell me I’m talking BS, just whatever…
EDIT: Aha! Here we are: http://en.wikipedia.org/wiki/Voiceless_palatal_fricative (/ç/)
It’s not just a plain h as in the word “he/him”, it’s more like in the word “hue”. 人(ひと) is actually listed as the Japanese example of the phoneme :D