I wonder if HAL is merely programmed to keep one player in reserve without any programming logic as to which one?
Against a lefty starter, all 3 of my OF are set to be replaced in a platoon.
In this case, there were 3 available OF on the bench (Carr CF- set to platoon v R for Walton)(E Davis, LF, CF, RF set to platoon at LF)(D Martinez RF, CF set to platoon in RF).
The CF (Walton) came up first. I had him set to be replaced by Carr. HAL left Carr on the bench and continued to bat Walton v R.
Next up was the LF (Hubbard), HAL correctly replaced him with Davis.
Next up was the RF (Ochoa). I had him set to be replaced by Martinez. HAL left Martinez on the bench and continued to bat Ochoa v R.
So, when Walton came up, there were 3 reserves available for CF but HAL did not make the platoon substitution. So it is not as simple as keeping one player in reserve.