Wifi Channel 6 is centered at 2437Mhz and is 22Mhz large, so ranging from 2426 to 2448 as you stated (well that would rather be 23Mhz large, so not sure if it is 2427-2448 or 2426-2447).
But data is actually transmitted along a 20 MHz bandwidth, the remaining 2Mhz are used as a guard band so there's enough attenuation along the edge channel.
So there's no data transmitted at 2426 Mhz when using Wifi Channels 1 or 6 (1, 6 and 11 are the most used since they are non-overlapping)
From Argenox
LE uses 40 1MHz wide channels, numbered 0 to 39. Each is separated by
2MHz.
Channels 37, 38, and 39 are used only for sending advertisement
packets. The rest are used for data exchange during a connection.
We’re interested in what’s happening in these 3 channels, and that’s
what we’ll cover here.
During BLE advertisement, a BLE Peripheral device transmits packets on
the 3 advertising channels one after the other. A Central device
scanning for devices or beacons will listen to those channels for the
advertising packets, which helps it discover devices nearby.
Channels 37, 38 and 39 are spread across the 2.4GHz spectrum on
purpose. 37 and 39 are the first and last channels in the band, while
38 is in the middle. If any single advertising channel is blocked, the
other channels are likely to be free since they’re separated by quite
a few MHz of bandwidth.
This is especially true since most other devices that interfer with
BLE are narrow band. Channel 38 in particular was placed between Wi-Fi
channels 1 and 6 so it avoids the Wi-Fi signal. The wide spacing of
the advertisement channels helps BLE better manage the interference
from Wi-Fi, Classic Bluetooth, Microwaves, Baby Monitors, etc to
ensure that advertisements succeed.
You may find this study relevant to your question:
Coexistence and Interference Tests on a Bluetooth Low Energy Front-End
Here are some parts:
On other hand Wi-Fi signals will see Bluetooth as narrow band
interference and only in the cases that the Bluetooth interference
is not more than 10 dB below the Wi-Fi signal can occasionally
cause interference. In most cases Wi-Fi transmits 20 dBm and
Bluetooth transmits 0 dBm so if we take into account the path
loss Friis equation of the transmitted Wi-Fi signal
Lpath= −27.55dB +20 log (2.4MHz ) +20×log[dist(m)]
and the Link Budget equation
Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) −
Losses (dB) − Lpath
We get to the theoretically conclusion that only
if the Wi-Fi Router is more than 3 meters away from the
connecting equipment and the Bluetooth equipment is on a 3 meters
area around the Wi-Fi equipment, that occasionally the Bluetooth
signal can cause interference over the Wi-Fi
The study conclude that:
C. Coexistence with Wi-Fi Due to their dependence on the same
band, the potential for interference exists. Therefore it is
important to see if there is interference from Wi-Fi on the
BLE transmissions. The results show no effect on the Bit Error Rate
or RSSI readout, in fact the RSSI readout shows that the value
increases. The results obtained show that BLE hopping is
effectively avoiding the Wi-Fi occupy channels, therefore there
is very good coexistence between BLE and Wi-Fi.
