well, ithink you still do not get my point...
- in
saam jin sau you move - the technique is about movement, it is not an isometric exercise (ie. against external resistance without any movement, although we do drills like that - with the partner, against the wall etc.)
- you can tense the forearm without bending the wrist (we do not do that)
- you can bend your wrist and tense your forearm (we do not do that - try and tell me what your upper amr and shoulder does, ok) because principle of muscular tension irradiation certainly applies, but this is not the aim of this particular exercise (and we have exercises where we extensvley use this concept)
- the rest above!
in a person you would understand in a couple of minutes. it is hard to explain in the words how an orange tastes, moreover, i really do not want to teach on the forum (heart to heart transmission, as Daatmou said

). the brief description above are just couple of notes.