Framerate drop when Chaos Destruction is offscreen

I have been messing about with the twin stick/top down template (in 5.6.1) and noticed that if i trigger the chaos destruction on a large group of enemies (25-30) and then move offscreen when they are destroyed there is a masive drop in frames versus staying on the screen with the destruction taking place.

When staying on screen there is typically a drop of around 30fps but it i move the destruction off screen there is usually a much bigger drop 70-120fps.

I have not really used the chaos destruction much and this may expected but i just wondered if anyone has seen this before or know what causes this.

This is not an urgent issue as i may not even use chaos destruction or at least not on this many enemies at once, i’m more just curious.