Well, yes. But understand that it is a logarithmic units. Negative numbers indicate decimals, and the more negative you get, the more decimal places. -90 is one billionth of a milliwatt (.000 000 000 001 mW), while -100 is one ten billionth of a milliwatt (.000 000 000 000 1 mW). -100 dBm is about twice as strong as -103 dBm.