Currently, if you shift-attack enemies, with most units they will kill the first target then move on to the next and so son. But Keeps don’t do that. Keeps only attack the latest target even if the display shows that they are supposed to hit the previous targets. This means you have to manually ######## each time the Keep kills a model so that it correctly targets enemies with low armor at the back.
Please add a Castle (or even Imperial) upgrade that lets you fully control the Keep’s targeting trajectory and decide in advance who it is shooting at without using so much micro.