The signal 'meter' on my phone often jumps around on networks.
If you want a better measurement of that actual signal from the AP, I would suggest running a program like inSSIDer on a laptop and graphing over time. That will show you what the AP is actually doing (or not doing).
Also, when you run such a test... disable ARM scanning, or you will see 'dips' in the RF output when the AP (rightly...) goes off channel to scan the air.
JF