Just carried out this tutorial using the latest version of the game and the sensor section didn't seem to match the description in the tutorial.
The Sensor Range calculation was changed. It now uses EM Sensitivity / 10 as part of the calculation. So:
Sensor Range = Sensor Strength x Sensor Size x Sensor Resolution
x (EM Sensitivity / 10) x 10,000
Since the EM Sensor Sensitivity for the designed active sensor is 5 (and 5/10 = 0.5), that reduces the maximum range from 20m km, to 10m km.
Since this is just a tutorial, I used the suggested hull size of 2 and resolution of 100 (5000 tons), so my sensors have the 10m km range. I don't know how that will affect things, but I'll find out
I didn't want the hull size of the active sensor messing up ship size calculations further along in the tutorial, and I figured that was more important than the maximum range.