to the op, it's more that we have no choice in shinkyokushin but to utilise kicks from all distances since pretty much all fights are in the 'pocket', toe to toe as close as elbow distance a lot of the times. compared to a muay thai kick, you still use the hip but it's more a snap and the angle you drive your leg into their leg if you get what I mean but also knowing what part of the quads to strike with. so you're kinda snapping/striking downwards but in a 45 degree angle in a way. practice would probably be the best explanation haha.
'head kick in jeans'
it's as simple as head kicking with shorts.... obviously not as comfortable but unless you're wearing tighter jeans that my girl's (than you should stick to ballet dancing), I don't see how there's any difference.
kicking range is longer than a punch or an elbows fyi....