Not a bad sensor — this is what they all do until they are set up, and the reason is inherent to how they work.
A millimetre-wave sensor detects motion of any kind, at very high sensitivity. That is its advantage over a passive infrared sensor: it sees the movement of your chest as you breathe, which is why it holds presence while you sit still. But it does not know what a person is. A rotating fan blade, a curtain in a draught, a plant in a breeze and a person are all moving objects reflecting radio energy back.
And radio at these frequencies passes through plasterboard, wood and glass. A passive infrared sensor cannot see through a wall because it detects infrared, which walls block. Yours can, which is why it sees the corridor.
So the tuning problem is: keep the sensitivity that makes it useful, while excluding everything that is not a person. Four levers, in the order I would use them:
1. Placement first, before any setting. This does more than all the configuration combined.
- Do not point it at a fan, a heater, a radiator, a curtain, an air conditioning outlet or a window. Anything that moves periodically will trigger it forever.
- Mind what is behind the wall it faces. Corridors, stairs, the neighbour's room. If the sensor faces an interior wall with traffic behind it, you will fight that permanently.
- Ceiling mounting is usually better than wall mounting, because it points down into the room rather than across it and through the far wall.
- Keep it away from large metal surfaces, which reflect and produce detections from odd directions.
2. Detection zones, not just distance. You mention setting a distance, which is the crude version. Most of these sensors support zones — a region defined by distance and angle — and often exclusion zones you can subtract. That is what lets you keep the room and drop the doorway. If your sensor's integration only exposes a single distance number, check whether it has a configuration tool or app that exposes the full zone model; many do, and it is not surfaced by the basic integration.
3. Separate sensitivities. These sensors typically distinguish movement from micro-movement (breathing, small shifts) and let you set each independently. The micro-movement sensitivity is what catches the fan and the curtain. Lower that one substantially and leave movement sensitivity high — you keep reliable detection of a person entering, and lose the phantom presence.
Some also expose per-gate sensitivity, meaning per distance band, which lets you desensitise exactly the band your fan sits in. That is the precise tool for your fan problem.
4. Only then, logic in your automation. Delays and confirmation windows, as a last resort. Do not start here — a delay applied to a sensor that is wrong is just a slower wrong.
A quick note on the three-in-the-morning case, because that one is usually not the sensor at all: pair the lights with a lux condition, so presence at night does not turn on a bright ceiling light, and keep a separate low-brightness night behaviour. Even a perfectly-tuned sensor should not put full lights on at three in the morning.