I thought that it had to do a bit with the MOB and/or enemy player level as well as the level of the infiltrator.
Example: A level 50 infiltrator with 45 stealth and +10 to stealth would be a level 50 stealth when up against a level 50 player and when the infi was up against a level 40 player they would be 45 stealth but when the infi was up against a level 55+++ mob the infiltrator would have an effective 55 stealth.
So, a level 39 infiltrator with 35 stealth + 10 to stealth would have 39 stealth when up against other level 39 players but if the level 39 infi went to the frontiers, up against a level 50 player the level 39 infi would have an effective stealth of 45.
-----signature-----
The art of war is simple enough. Find out where your enemy is.
Get at him as soon as you can. Strike him as hard as you can,
and keep moving. - Ulysses S. Grant
Only the dead have seen the end of war - Plato