What would be the use case for limiting advertising to a single channel ? It is generally discouraged except for power saving if the battery has to last for several years.
I’m not sure to follow, advertising on a single channel will likely increase scanning time for central, not reduce it. It saves power on the advertiser at the expense of the scanner that will have to spend more time scanning over the 3 advertising channels to find the device.
AFAIK there is no API to use it with the legacy API.
The real world is very noisy. Savings in a lab might prove not worth it. The advertising channels are spread out on purpose with a busy environments in mind (2.4 channels nowadays are really busy).
Even if it was the case (AFAIK it isn’t), how would that help ?
The scanner moves from one channel to the others periodically, there’s little guarantee it will start scanning when the advertiser is emitting and it doesn’t wait for it either to listen to another advertising channel.