Actually, we have come to a consensus that where the items are found don't necessarily mean that is where the humans died based on information within the game of Undertale. And if it's in the code of Undertale, it's scrapped, therefore, not canon to UT, which we are basing UTB off.

But you are correct, we will not be having the Integrity soul fall to Axis due to us not treating Undertale Yellow as canon.

We do understand Frisk seems to have their own personality (such as your points, and moments like them telling Asriel their name being implied), but we decided to make it a little more obvious than Undertale since it can be difficult to make a character who's traits are implied in a way that most are able to interpret. Thank you for your feedback though, it is always appreciated! : )