The lengths need to be the same; tank and carto.
The Smoktech tanks use a flange at the bottom end (connector side). I think I remember reading somewhere if you use a non-flanged carto on a DCT-type tank, you should turn it upside down (top side of tank to the battery connector). These tanks have a slight "cut away" or depression in the bottom endcap that the flange of the DCT carto rests against. I don't know cause I've never done it, but it may be using a regular carto (without flipping the tank) could cause some leakage (?).