Note that the "cutoff frequency" definition linked from there has a typo: -3dB is 10^-0.3 or 50.1%, not 70.1%.
IANAJ(*) but as I understand it, the "-3dB" refers to 50.1% of the size of the effect at the centre frequency, not 50.1% of the output response. So if your gain on a particular EQ channel is +2dB of the output response, the "-3dB points" of that channel are where the effect on the output response is 50.1%, or half that: in other words, the frequencies where the effect on the output response is +1dB.
This means that any adjustment has some effect beyond the -3dB points. Indeed, any adjustment theoretically affects the entire audio spectrum, though the effects become negligible at any great frequency distance from the centre. Quite how rapidly they fall off (for instance, where the -6dB points are) depends on the exact shape of the filter.
As a concrete example, if you have an EQ band centred on 100Hz, with gain of 4dB and Q of two octaves, the boost would be +4dB at 100Hz, +2dB at 50Hz, and also +2dB at 200Hz. Frequencies just below 50Hz would be boosted by just less than 2dB, as would frequencies just above 200Hz.
Interpreting the "-3dB points" to mean "the places where 3db less difference is made to the output response" would make Q meaningless for EQ bands whose centre gain was smaller than 3dB.
Peter
(*) I Am Not A John, or, put differently, I'm not one of Empeg's two EQ gurus.
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