I'm borrowing a friend's Canyon Grail (with Shimano 105 groupset) and in some gearings there's inevitably chain rub. He says that he's found that, with brifters (instead of bar-end shifting that would give a tension option), there's basically no way to calibrate the indexing such that no gearing suffers from chain rub. Some combination of front and rear sprockets will inevitably rub. Is that difficulty idiosyncratic to his setup or is it just generally a problem with 105 shifting/gearing systems?

Thanks for any insight!