it could burn, and/or inhibit rooting by forming too much callus

Unless you are doing hardwoods the .1% will be fine. Gardeners tend to think hormone is needed much more than it really is. Al

I think OP has an excellent question and would like to see some links to academic answers.

Having said that, I think calistoga's advice is probably as good as armatures are going to get.

I believe Calistoga has hit the nail on the head. IBA is certainly useful, but I believe other factors are equally important. Time of year as well as time of day are quite important and many somewhat difficult rootings may be sucesfully effected by very careful adherence to these two factors. Pure IBA is relatively inexpensive, but the commercial preparations are all relatively useful. Any current text on plant physiology is even more useful!!!