Hi,
The Snap Point is the stemp in the file, where did you really pressed the Record button. The signal ahead is the signal, which had been recorded before your started the track Record (Cubase offers you to don’t miss something important, if you hit it too late).
Obviously the expectation is, you want to operate with the time, when did you really pressed Record button. If you made a mistake and you pressed the Record too late, move the Snap Point (marker/flag) to the wanted time stamp, please.