Issue with Interpreting Yield Calculation from Yield Curve

[gsharma007]

We consider two types of Yield Curve.
Yield Curve 1 depicts fast processing, which means the sample's overall time in the service is less
Yield Curve 2 depicts slow processing, which means the sample's overall time in the process is high

Now for each sample/therapy/patient, we have to allocate some time. Either that patient is in slow processing or fast processing. Either T is low or T is high.

Questions:
a) As per our graph, the yield is maximum when the yield is equal to Ybar. So where is the problem in understanding? How the Y will exceed Ybar?
b) If we only have times relating to fast or slow processing, then where is normal processing? Why are we not considering that case here?
c) When we talk about product policy i.e. % of the sample in fast, normal, or slow processing. Is that similar to the patient mix policy where we define the % of patients to be good, average or bad?

It may be possible that the yield curve combines with the product policy to finalize the time of processing or maybe we just consider all samples in fast processing in case 1 and all samples in slow processing in case 2. The later makes more sense.

Possible Flow:
Factor implemented -> processing time based on level -> yield value based on processing time