I was just searching for an answer to this exact question, come to find out the command itself adjusts the buffer!
mode con:cols=140 lines=70
The lines=70 part actually adjusts the Height in the ‘Screen Buffer Size’ setting, NOT the Height in the ‘Window Size’ setting.
Easily proven by running the command with a setting for ‘lines=2500’ (or whatever buffer you want) and then check the ‘Properties’ of the window, you’ll see that indeed the buffer is now set to 2500.
My batch script ends up looking like this:
@echo off cmd "mode con:cols=140 lines=2500"