Apologies if this is evident to others, or if it's already been answered, but I had a question about replacement level.

I was reading an article I believe at FanGraphs discussing the value of closers (maybe in regards to the Joe Nathan injury?).  They made the argument that replacement level for closers is different than it is for other positions.  The argument was that you don't replace the closer with freely available AAAA type talent.  You replace the closer with the eighth inning guy, replace the eighth inning guy with the seventh inning guy and so on until you're replacing the long reliever with the mopup guy and the actual replacement level reliever gets inserted into the the mopup job.  This makes sense to me, but it led to two questions:

1.  In determining the replacement level for a closer, is it appropriate to just compare the closer to the eighth inning guy?  Would it not be something more like (closer minus eighth inning guy) plus (mopup guy minus 'true' replacement level guy)?  It seems like just using the eighth inning guy fails to account at all for the new man in the pen.

2.  Would positions players not operate the same way?  Would you replace a starting outfielder with your AAAA outfielder or would you replace your starting outfielder with your fourth outfielder, and replace your fourth outfielder with the AAAA guy?  Put another way, would you replace your number 1 outfielder with your number 5 outfielder OR replace your number 1 outfielder with your number 4, and replace number 4 with number 5?  I probably could have worded that better, but the same principal to replacing best reliever with second best reliever would apply to replacing best outfielder with next best outfielder and so on down the depth chart.

If that is the case, then wouldn't the replacement level 'value' for an outfielder be the fourth outfielder, the replacement level 'value' for an infielder be the utility infielder, etc? 

Perhaps this is accounted for in the calculation of replacement level.  In which case, disregard my ignorance.