Sensor Range is no longer a flat linear number, like Speed is. This is because the AREA a sensor sweeps out is just as important as the linear range. Sticking with a linear range meant that every increase in Sensor Range brought a increasing amount of area with it, which is seriously OP. For example, a +10% bonus to Range actually increases the total area seen by 20% (1.10^2)
Rather, the new concept of "SensorPower" was introduced, which attempts to take into account this problem. In order to have a Range of X, the arithmetic sum of X in SensorPower is required. The math is such:
SensorPower required = (Range)*(Range +1)/2
All bonuses are now to Sensor Power. So, a +10% bonus to SensorPower is much less likely to increase Range. In particular, small bonuses are unlikely to change Range except at the very low end (when you have NO sensors) or when you're near a boundary (i.e. when the SensorPower you have installed isn't quite enough to make the cuttoff for the next Range).
In short, Sensor Bonuses in percentage will generally only provide a +1 Range for those ships with no sensors (even for very large bonuses). For those ships with moderate Sensor Range (ie. 4-7 or so), these will be the ones which you see the biggest benefit from, with large SensorPower % bonuses translating into 2-4 extra Range. Once you get about about 10 "native" Range, you are really going to need about +25% or so to see a +1 Range bonus.
Sensor bonuses make the most impact for ships with 2-3 sensors on them. Below that, you'll either see +1 or none, no matter how much additional bonus you research. Above that, you'll occasionally see a +1 range, but it won't happen with every additional Sensor bonus.
It's all about the math. 
