Upper arm above the elbow, same as you.
The sensor will still have similar struggles as a wrist based OHR sensor. It will have to figure out which of the many signals it detects in the skin reflectivity is the change in blood volume (and not sensor movement, muscle contractions, stray light, etc) and keep tracking it. Moving the sensor to the upper arm from the wrist does reduce the false signals significantly, making the blood volume changes easier to detect and track.
But how detectable the blood volume changes are in the first place, how strong the false signals are and how much the false signals are attenuated by moving the sensor to the upper arm is going to vary from one person to another. For some individuals it may even be possible to get very reliable heart rate measurements from the wrist with a good sensor while cycling. For others it may be hard to get reliable readings even from the upper arm.
In any case, I only see a handful of errors per season with the OH1, and I do well over a hundred workouts per season.