ICU,
As the others have elluded to, the generic satellite meters are non-discriminatory. Meaning that if you were searching for satellite 123W, you could have dialed your dish in on 121W or 125W or even further off than that and this signal finder will tell you that you have a strong signal. It also does not look at just one TP signal from the satellite, it looks at a composite signal of every TP on the satellite. Then, when you go back to the receiver and try to scan 123W, you get nothing, because you are not aligned with 123W at all.
As others have posted, and I am in total agreement and recommend it highly, the best way and the most inexpensive way, is to use a portable TV and your sat receiver out at the dish directly. Here, you can set it up to monitor a specific TP on a specific SAT and when you get a LOCK, you are assured to be on the correct and intended satellite. The signal finder that you are using is very handy for getting you in the ball park quickly - in other words it is very handy to rough it in as it will be quicker to respond to the signal from the sat whereas the sat receiver might take a few seconds to lock on and display a signal reading.
If your receiver's signal/quality meter is one that is overly sensitive or "jumpy" or if it is not sensitive enough and doesn't update quickly, then the signal finder you have will be very handy as you can detect immediate and accurate changes in the signal strength as you try to peak your dish alignments, so it is extremely useful in this regard, especially since it provides an analog readout rather than a digital representation of the signal.
Therefore, you are not doing anything incorrectly in the use of this satellite signal finder, you simply aren't doing everything that you need to do.
RADAR