Here's a simple case involving only 3 change sets which illustrate when you can't suspend one particular change set out of the top 2, without suspending both of them.
We'll assume that we're starting at some change set called CS0.
Step 1: Modify fileA.txt --> Check-in to CS1 --> Complete CS1 --> suspend CS1 (CS1 states: 1 --> 2)
Step 2: Modify fileA.txt --> Check-in to CS2 --> Complete CS2 --> (CS2 states: 1 --> 3)
Step 3: Resume CS1 --> This results in a conflict and a new merges change set CS3 --> Choose "Resolve with Mine" (CS3 states: (1, 2) --> 3)
The order of the change sets in the history is now:  CS0, CS2, CS1, CS3.
The merge graph looks like:
[CS3]
  '      \
  '        \
  '          |
[CS1]    |
  |          |
  |       [CS2]
  |     /
  |  /
[CS0]

-Trying to suspend CS3 would result in a fork conflict since CS1 and CS3 have two different end states (This doesn't make sense in a history, so this is not allowed.  Remember that CS3 was automatically created as a merge change set when accepting CS1 to resolve this).
-Trying to suspend CS1 cannot be done either as this would create a gap in history.
-You can however suspend CS3 and CS1 both at the same time, leaving only CS2.