I share your concerns, Lars. One of the situations that made me want to revamp the HTH rules was having a player insist that he could initiate HTH in movement and then make an attack on the same turn as his action.
My house HTH rules on my occasional blog,
Musings from Myriangia. These state that attempting to initiate HTH is
always and action, regardless of your engagement status at the beginning of the turn the attempt is made. I've also added some new options and conditions that I hope add to the realism. I'll admit that I've had a player chafe at the idea that making HTH initiation an action sort of looks like someone running up to tackle a foe, stopping when adjacent, waiting for their turn to act, and then tackling. But I maintain that this is all just due to the game conveniently modeling combat with everything more or less happening at once.