I agree that this is a difficult problem. It seems to be that way because the incentive structure is misaligned for truth. The costs of giving someone unbiased feedback are mostly paid by the giver of the feedback, but the benefits are mostly received by the receiver of the feedback. Thus, this is very difficult to get from people who are not close friends and allies- but those people are probably ones who have an above-average view of you.

Thus, one of the low-hanging fruit here is rewarding negative feedback, which is in many ways more useful than positive feedback (and yet most people don't reward it).

It may be useful to ask people you trust questions like "How do you think other people view me?" The deflection to other people makes it easier to voice their personal concerns under plausible deniability, as well at getting at the question of "how do I present myself to others?" and "what features of my personality and behavior are most salient?"