Here's the spacing I've found to work and still fire effectively, 19 tiles from the statue. The only ideas I've been able muster to stop the engine is either a simple active block strip/actuated blocks, a drop into a lava trap or possibly a hoik past the statue to a lava strip on the left.
So far I've just been cutting the wire to turn it off but that's tiresome.
So far I've just been cutting the wire to turn it off but that's tiresome.