AirPort Extreme Question: 17" iMac/12" PowerBook

[Balin64]

Hey Guys:

I have a 17" 1Ghz iMac connected to a cable modem. I just got it, and it came with a bad AirPort Extreme extender cable. It was replaced, so I can finally check out AirPort extreme with my AlBook. Here's my question: I am sharing the cable modem connection with my 12" 867 PowerBook. The iMac is in the corner of my living room, and if I take my PowerBook into the kitchen, about 20 feet away, with only a wall with open doorway in between, the AirPort status loses one bar. The weird thing is that I used to do the same thing with a G4 500 tower (in my bedroom, about 45 feet from kitchen) and a 700 iBook and I always got a full signal strength. Does the iMac case reduce the signal? I know that in the 17" iGhz model the antennas are in the dome and not the display. I also have "Interference robustness" turned off. Does anyone have the same two systems and similar residential layout? What are your experiences? Any comments greatly appreciated, it's just that after getting a brand new iMac and having the AirPort Extreme in it tinkled with at the shop, I want to make sure this is normal range, or if I need to pursue the matter further. Should I be worried? Thoughts?