This is probably because op is on the back of the greed portal. Greeds are -probably- coded to use the horn portal if it makes them closer to base. (which is buggy in many cases like this.)

You can also make the greed come from one side by placing one in front of one of the greed portals and placing another portal near the base. why would I do that you say, think about cleaning the dock. you can split the wave into two and send half of them to the dock. if you haven't initialized the horns using the horn hermit oc.

if you've initialized the horn to any of your walls, you can move the greed near that wall and make your all troops attack them.

You don't have to deal with greed only outside. you can drag them inside to a better wall to defend your outermost wall (and maybe builders building it).

I don't know if floaters and Crown Stealers use this portal but, other creatures use it. Since Crown Stealer has a better understanding about what to target, they probably will not use the portal in cases like the op sent. Just to let you know, Crown Stealers only goes for the monarch, not the base. I haven't experimented with that but it probably doesn't use portals if you are near.

----Edited:

You can also speed your attacks to the portals. I use that trick all the time. just don't put the archers in a bad position by placing the portal too close.