Are you racing with the Notio Konect actually attached? I'd consider both the Konect and speed sensor to be essentially test apparatus to be used for measuring, with both removed on race day. And you'd just hope that that the test apparatus don't interfere with the results much.

How do you know that it will cost you a few watts? It's partially shielded by the tire/rim and spokes.

Unless its integrated into the frame like the Bontrager speedtrap was on some Trek bikes it probably will have some drag.

The 1 time I did some aero testing at a velodrome I used one of the older style that zip ties to the chainstay and uses a magnet on the spokes. I had one of the magnetless garmin ones, but the person running the test said we should use the older style one. I don't remember the reasoning for that.

Is there a reason you need 0 drag from the sensor. I would think most people are interested in relative differences in drag. As long as the drag from the sensor is constant you should be able to use your data to determine if changes in position and equipment add or reduce drag.

Some potential reasons are mentioned by Garmin here: https://support.garmin.com/...L91YJSJd3Tnyif9jRSy6

I do prefer the older style one since it's accurate and less susceptible to environmental noises.

I have mine on the rear wheel. I don't think it'd have much of an aerodynamic impact at that location. I assume airflow is already dirty (turbulent) at the rear hub.

I would worry more about picking a sensor that is reliable. I've seen people obsess and argue about the placement of their sensor, One guy put it below the chainstay, closest to the crank as possible. His argument was that it was shielded by the crank. It was the Garmin unit the magnet (GSC10). He had a ton of dropouts.

I personally use the wahoo that goes on the front hub. The SRM on rear of the front fork works well when you don't have a regular hub (a la trispoke). The SRM had less dropouts than the Garmin so maybe it would work on the crank side under the chain stay.

But I think you're slicing hairs. Better to get reliable data.

To quote Swiss Sides Jean Paul Ballard:

"Don’t put your Garmin wireless speed sensor on your front hub! Quite often we notice that cyclists fit this sensor on their front hub. As we have often reported, the front hub is an important part of the aerodynamics of a wheel. Fitting the speed sensor unit to your front hub will cost you 1 Watt of performance! We recommend putting it on your rear hub where the impact is minimal".

https://www.youtube.com/watch?v=SRkpAJvdC1o