Lets start with the Lambert Beer's law, A=(epsilon).(concentration).(path length)
Since epsilon (absorption coefficient) and path length are constant for the same sample and cuvette, absorbance is proportional to concentration. Thus increase in concentration of your extract should linearly increase the absorbance. Please make sure that maximum absorbance of the sample does not exceed 1.0, since at higher concentration (absorbance) non-linearity might take place. You might find this link helpful