Yeah Ahill, there are two types of Kiai; though the series nor the guidebooks go into detail about it. One actual exists in real life and is the mere act of releasing all your power with a yell, the other is the embellishment made by Dragon Ball where characters push things alway with invisible Ki waves. Tenshinhan used the former to deflect the Kamehameha, and the Kikoho fits the bill for the later.
[mention]SuperSaiyan2[/mention] what you make of Gohan >> Oozaru Goku? You suppose Goku’s size and/or Gohan not wanting to hurt him were factors? Though he knows about the tail weakness, so that may not be a factor.