ISdev and ESdev clarification

Hi all,
I am a bit confused with the concepts behind ISdev and ESdev and their relations with ISim and Esim. For example, if I have two clustering solutions:
Solution 1 with higher internal similarities, lower external similarities, but also higher standard deviations (ISdev and ESdev) .
Solution 2 with lower internal similarities, higher external similarities and lower standard deviations.
1) Which of the two should be preferred?
2) The coexistence of high ISim and high ISdev values could be explained by the fact that ISim considers the pair-wise similarity between objects, while ISdev considers the deviation from the mean point?

From my understanding:
-ISim indicates how cohesive the clusters are (higher values are better)
-Esim indicates how separated the clusters are (lower values are better)
- ISdev indicates how disperse the objects within a cluster are (lower values are better)
-ESdev indicates how disperse the objects between the different clusters are (higher values are better)
2) Is the above correct?
I would be very very grateful if somebody could help. Many thanks in advance!