My Barriss cantina farm drop rate is very high.
My hard node farming is probably near 30% lately. Rey hasn't given me any shards in a few days, but I did have a 4 and 6 shard day in the past week.
There may be code that lowers drop rates based upon certain factors, I really have no idea; but the best thing CG could do would be to write the code and break RNG for cold streaks.
Hot streaks gain them good will. I wouldn't mess with those. Preventing long farming droughts by increasing the chances of drops after every miss (to be reset once an item drops) would go a long way.