Maybe you should allow to fight defensively while preparing, simulating the fighter waiting for an opening in foe's defense. I am not sure if this should be reflected by an initiative bonus or an AB bonus though.
I was about to suggest using boon points to gain initiative, but it's already there... IMO, that's a good way to reflect who has the edge during a fight.
Finally, most of us (including you Tim) seem to prefer rolling once and then only when significant changes happen. I see the logic behind this, but making one roll per combat makes more room for hasard regarding initiative. Rolling only once, if a very quick character rolls very low, he will be constantly behind the slowest characters (I mean those with low speed bonus). Rolling multiple times gives more weight to stat bonuses. That way, quick characters will generally go before slow ones.