I do use the graphs, but I wanted more solid, calculable numbers to compare, so I ran a few tests as Athanor suggested and I'm getting roughly the same results for both games, for example: 9 UFOs by Feb, 20 by March, 29 by April in UFO/EU; and 9, 16, 31 in TFTD, respectively.
The issue may then be TFTD's lower detection range:
Standard Sonar
radarRange: 1500
Wide Array Sonar
radarRange: 2250
Transmission Resolver
radarRange: 2400
Whereas UFO/EU is:
Small Radar
radarRange: 1695
Large Radar
radarRange: 2577
Hyper-wave Decoder
radarRange: 2759
And the "fix" would obviously be: bring up TFTD's detection range to UFO/EU standards.
On a sidenote, anyone know if the range (nautical miles for UFO/EU and kilometers for TFTD) as described in UFOpedia is accurate?