If the crosstalk is in phase it will tend to reduce the image width, but if it's out of phase it will tend to widen it. Sometimes that can be helpful, especially as it tends to be a frequency-conscious effect, generally getting stronger at higher frequencies.

What is good crosstalk?

Good values for crosstalk in electronic devices range from 50 dB upwards, with crosstalk in excess of 100 dB achievable by sufficient isolation. When the application is stereo or surround sound, such values are far higher than really necessary for a full effect.

What are the effects of crosstalk?

When noise interferes with other circuits it is called crosstalk. Crosstalk can be transmitted through electromagnetic radiation or electrically coupling, such as when unwanted signals propagate on the power and ground planes or couple onto the adjacent circuits.