There's a reasoned explanation of attenuation between street cabinet and cable modem
here.
How far are you from the street cabinet? There are attenuation points of 12, 15, 18 & 22 dB (if my memory serves me correctly) from which an engineer can choose for your case. So the highest leaving the tap point would be c. 30 dBmv (see the article) and then the losses on the way.