Though I'm too lazy to do "extensive testing", I can state that I'm under the impression that there is a bit of truth in Zels77's remark about leaders unevenly often getting hit.
In fact, there's another thing about leaders - and spotters - that has been quite remarkable in my perception. It seems that while playing the AI (I never played a human opponent), units with a spotting ability deploy more a often in a position where they CANNOT spot, than units that have no ability to call in arty.
For instance, when I deploy three squads and a HQunit randomly along a hedgerow, it still seems to me (after months and months of playing) that it is usually the HQunit that can't see the enemy on the other side of the field, while at least two of the squads can.
Maybe it's only my perception, or maybe I'm just brilliantly stupid at placing units, but it happens annoyingly often. In order to get mortarfire on the enemy, I need to replace the HQunit and hey, there goes another useless minute in which the enemy has just time enough to scoot.
So: Spottersunit spot less then others???