fun fact: for anyone who wants to draw saiibo, according to their canon heights, the top of kiibo's head (minus his hair) arrives approximately at shuichi's eye level
so no, kiibo isn't nearly one head smaller than him. if you want two characters who have a bit more than one head of height difference, look for oumota! (the top of kokichi's head reaches around the bottom of kaito's neck) not even saimota has that much difference (the top of shuichi's head is around kaito's nose)
saiibo has 11 cm difference, saimota has 13 cm, and oumota has 28 cm difference, while a head (i measured my own-) is around 25 cm.
i'm not saying anyone who doesn't do that is wrong or anything, i've probably messed up saiibo's heights many times. and if some people just don't want to draw them at their canon heights it's also completely ok! i just thought of sharing this bit of info in case someone needs it!
p.s.: i decided to look at my saiibo art and i realized that if i didn't respect what i said above, actually, sometimes i even made kiibo too tall. hm.
p.p.s.: i could've included other ships but frankly, i'm tired, it's almost 5 am so i'll just do these three. if you want other ships, feel free to ask me, or pick up your faves' wiki page and a ruler to measure their differences yourself!