killing Shade the moment it appeared as a tile in the monolith.
This might be the problem. The drop rates of the Shade's rarer uniques are higher the further the shade echo is from the centre, so repeatedly running ones close to the centre isn't necessarily the quickest way to find them. On top of that the drop rates are higher at higher corruption.
It's difficult to know how much we should telegraph drop rate information like this in game, but we're not necessarily opposed to making it clearer, and situations like this are taken into consideration for making these sorts of decisions.