Help understanding used power

Hi, list!

I'm trying to understand how the options "nominal power" and "max_power_red" work...

Last Friday I tried to place 4 BTS in a rectangle of about 100x20 meter and then I examined the measurement reports of a mobile. They are very very bad, and oft it cannot see a cell. Then I tried to change the value of "nominal power" (max_power_red did not changed) and retry to check the measurement reports. No changes... :(

Now I'm here in my office with a spectrum analyzer and try to change these values, but what I see in the spectrum analyzer is always the same... I restart OpenBSC after any change, of course!

Could you please help me to understand what these values mean and how can I boost the signal?

Thanks a lot in advance for your help!