If someone don't understand the purpose of this "red L lever" in the drawing:
The red lever under throttle grip is for bi-pass the the stop/detend near end or throttle course.
This "stop" purpose is simulate the 'gate'* of some WW2 era throttles that need be overcome for engage boost/WEP, similar of some modern jet's the "afterburner" detent
The mechanism purposed is based on the one used in Mig-21 throttle lever for by-pass the stop before afterburner range, is choose because don't require changes in the other parts of the throttle.
Now with WW2 games using more detailed engine operation, the Emergency Power is controlled by throttle course instead that generic "gamey" WEP key of early IL-2, for example in Bf 109 of IL-2 Bo'X the rated power is up to around ~83% of throttle course, after this is engaged the Emergency Power.
The purposed "stop" is for avoid player engage Emergency Power inadvertently.
* The 'gate' in WW2 era throttles generally require force the throttle lever for left for by-pass a small 'steep'. Example of this 'steep' in Hawker Typhoon throttle. http://spitfirespares.co.uk/Website%20products%20501/T%20Cover%201%20large.jpghttp://spitfirespares.co.uk/Website%20products%20501/throttle%201%20large.jpghttp://spitfirespares.co.uk/Website%20products%20501/throttle2%20large.jpg
Force throttle lever for left in domestic throttle is not practical, in the "heat of the battle" the virtual pilot probable end tilt the entire throttle.