First, this is Poweramp player forum category, not Equalizer, so I’ll move the topic appropriately.
As for very precise low frequency bands tweaking in Equalizer it may require increasing Block size to increase resolution of the FFT used in Equalizer app. The whole processed spectrum is evenly divided, and while Equalizer tries to approximate parametric/graphic bands/settings to these fixed FFT bands, you may have like 10hz+ or so resolution, which may not be enough for 100% accurate lower bands.
Increasing block size increases resolution, but it also increases cpu load and smearing, so there is a trade off.