What is full scale of flash ADC?
SQRN is an |absolute value| (positive only) for AC signals and thus the reference is to zero and not negative peak or peak to peak.

if you do not amplify your input signal to full scale equal 0 to Vref, then your SQRN value for V, remains at 1V peak.  However if you do then your new Vmax= Vref/2

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