The problem with "acceptable losses" is you're dealing primarily with civilian perceptions which are most definitely NOT the same as military.
In general, and I stress this is the military viewpoint, the US Army considers a unit to be "combat ineffective" at around 25% casualties, the USMC at around 50%. The key here is the term "combat ineffective" not the number of casualties. It's felt that at these casualty percentages the loss of firepower, unit cohesion, and morale means the unit can no longer be expected to perform the mission a unit of a given size would be expected to perform.
For a US Army 9-man squad 25% is the loss of 2-3 men, the remaining 6-7 can no longer be expected to perform a full squads mission. The USMC squad is 13-men, so a loss of 50% still leaves it with 6-7 men ... the same size as the US Army squad with 25% losses. This is one of the reasons the USMC feels it can accept more losses (also the "Sturmtruppen" attitude of the USMC).
http://www.realcleardefense.com/arti...ry_108075.html
Civilians on the other hand tend to see losses of more then 5-10% as horrific. And I can understand this, imagine if 1-in-10 people near you died or were maimed in the next few minutes ... that's pretty devastating to the uninitiated.
Keep in mind WinSPMBT deals with military not civilian perceptions (and I've long felt the AI is secretly run by WW II Japanese).