I'm not sure how it worked in canon (and would expect semi-random behavior given Rowling's tendency to fudge world building details that a more mechanistic thinker might nail down) but in MoR it appears that legilimency allows the reader to perceive the "conscious surface thoughts" of the readee, plus the feeling of active reading (used by an occlumens to race ahead and put fake conscious surface thoughts in the way), plus the traces of past reading.

When Albus read Harry early in the story to look for traces he asked Harry what Harry had recently eaten so as to prevent himself from reading anything private in Harry's mind. If words can be used to redirect attention to banal issues so that it is impossible for even Albus to see more deeply, it stands to reason (to me anyway) that visibility is relatively shallow and that words could also be used to redirect attention towards the sensitive issues. So, HAC using legilimency probably couldn't get a verbal reason for lack of trust without a probe to raise "trust of HAC" in Hermione's mind, but once raised he would have been able to tell if she lied or detect any reasons that jumped into her mind that she didn't say out loud for strategic reasons... and not much more.

I could be wrong. "Word of god" might contradict me. But assuming I'm not, then my working model of the fic includes that HAC now knows, for example, that Harry has a deathly hallow (because Hermione would probably have consciously surfaced the most dramatic evidence that Harry totally trusts her when HAC asked about that stuff and that's pretty dramatic evidence). Given how many readers didn't even get that cycles of oblivation were being used on her I'd guess that something too optimized (to the point of silence) would be even less intelligible in text.

I guess a totally "optimized" oblivation/legilimency cycle could probably do a full loop within like 8 seconds and would just involve a "don't think of a polar bear" shout, reading everything brought up by that, then obliviate and repeat. We didn't see that happen at all. Either we didn't see it because it was impossible, or Eliezer didn't think of it, or Eliezer didn't think HAC would think of it, or it would have been too squicky and thereby violated the artistic permissions of the audience.

My bet is that this kind of manipulation would be impossible based on the in-story mechanics of legilimency and related spells... that the pragmatics of the process require a measure of indirection even with naive victims so that their eyes can't be closed, and their thoughts have time to percolate, and things only mentally accessible from within a specific conversational context can occur to them to be read, and so on.