Blowback is caused by the resistance of your moving downrigger weight against the water. The faster you go the more resistance, therefore the more blowback you will get. It will cause your weight, and lure, to run higher than the amount of cable you have out. Sometimes considerably higher.
Watch your cable angles this season at different speeds while you are trolling and it will be real obvious to you, Watch for cross angles caused by underwater currents also. It is usually not a good idea to raise or lower your riggers under the cross current conditions or you wll increase your odds of crossing your cables. The heavier and more streamlined your weights are the less blowback you will have. I fish with torpedo shaped weights especially when fishing deep.
Hope that helps.
Glen