I'm not using this system anymore, but yes I went from using 25mm to 32mm overflows. The whole point of the system was to have one running at full syphon and reducing the noise and the other taking as little as possible. During power failure test, water would rise and siphon tube would start to run, then second pipe would begin taking a lot of water but until the siphon purged all the air it wasn't taking its share of the flow. After the initial 20 secs the water level drops to the same level as the second overflow and is almost a trickle through it. That being said 9/10 times the siphon started fast enough to prevent any issues