Personally speaking I'm more inclined towards a holistic approach towards defending, limiting any discussion on defending to just the backline seems to be insufficient imho.
I haven't been using tight marking simply because, at the lowest echelons of league football, you just can't find the right players to do that kind of a job. What I prefer to employ is high closing down upfront, this forces the AI to spend less time on the ball, get my midfield to play more of a holding role and perhaps here is where tight marking can be employed.
At the back, the CD's will come up to mop those lose balls becos, regardless of what their closing down levels are, their defensive duties are more a function of the Defensive line. So if the defensive line is set too low..you'll find your CDs staying back more,but if they are set to the lowest notch of normal they do come out. Whether you have a split mentality for either DC does not seem to really matter here...the one closest to the ball seems to make the first move.
If the fullbacks have a closing down set of around 13-15, which is high, you'd find that if the ML/or MR is on 8-12. they will be some 2 on 1 action here. The question one has to ask, is whether this is what they want....I don't really mind that as much, cos I hate defending deep crosses. Can manmarking work...maybe..tho I must add my years of seeing it fail just act more as a hinderance to adopting it, and my lack of playing time recently has made it tougher.
I still think any discussion on defense cannot and should not just focus on the backline. A good defensive formation needs to account for the roles the forwards, midfielders and defenders do. You can make the 3 sets play as a team. If you can do that successfully then making the formation work is a cinch