Because there are 2 nodes in short distance to go to mini boss, so you need to have a high speed team to pass those 2 (speedy team tends to go farer than normal team). I did one auto run after this, and my 700 speed unit accidentally land on the mini boss (on the same pattern) but chance is slimmer on 700 speed. I think the higher speed the higher chance to land on it. There are many nods so it's easier to manage with two team (one should have high speed other on should not be stronger than the boss in case it pass the upper nod). Fortunately, i have 2 allies with speedy helper team.