^ Sure, but if it displays battery full at 4.2V, doubling battery capacity does not change that. IF it has to be calibrated to correctly display remaining charge once it has begun to discharge, doubling capacity does change that.
Apparently it is not the case that all tablets determine capacity by a voltage measurement alone. I wonder if this is due to issues like changing load, that it might sip power in a sleep state but rapidly consume it playing a game or video, causing a temporary voltage depression, but they don't want it shutting off, dimming the display, or other power saving strategies prematurely.
Battery calibration is a thing but we have no info about whether Pssdof's tablet does this and/or if any attempt had been made to calibrate it.