What factors will affect the CTR value of optocouplers?

(1) Optocoupler itself:
Taking 817 as an example, when CTR is at Ta=25 ℃/If=16mA, the range is (15%~35%). This indicates that for the optocoupler model 8701, no matter when/where, any sample in any batch, as long as Ta=25 ℃
/Under the condition of If=16mA, CTR is a definite value that can be determined within 15% to 35%. When calculating conductivity, the following limits should be applied and margin should be ensured. When calculating shutdown, the upper limit should be used.
(2) Shell temperature effect:
The lower limit of CTR under the condition of Ta=25 ℃ has been determined, but often the temperature range in the product is relatively large, such as the optocoupler working at (-5~75 ℃). How can CTR be determined in this situation? Still looking at the manual of 8701: There is a Ta CTR relationship diagram:
From the graph, it can be seen that with 25 degrees as the benchmark, under other unchanged conditions, the CTR at -5 degrees is about 0.9 times that at 25 degrees, and the minimum CTR at 75 degrees is the same as that at 25 degrees.
So under the condition of 16mA/(-5~75 ℃), the minimum CTR of 8701 is 15% * 0.9=13.5%
() 3) Affected by If.
Assuming that the actual If is 3.4mA, how to determine the minimum CTR value under the condition of If=3.4mA/Ta=(-5~75 ℃).