My main point would just be to try and keep the shelves and pairs of cables as much to a symetrical resistance as possible, unless I had separate fuses / breakers on each of the parallel runs. Probably could be fine to hook one (of each on the pair) on each end of bus bar as well (I just never tried it before). Would have to try and experiment with it to see if there is any apparent improvement.
My concern would be that connecting at two different points (onto the bus bar) with each wire of the pair, might cancel out the diagonal effect, but I'm not electrical engineer, and don't know the math, I would prefer to just put both cables of one conductor (of the pair) onto the same basic point (wherever I decided that to be) of a bus bar, unless I had separate fuses on both runs. I want the resistance to be as close to identical on the pair (to guarantee identical current flow), but that's just my preference.
If everything (cables, bus bars) is sized properly (not undersized), then it shouldn't really matter as much if at all (reducing the chance for resistance bottlenecks).