I believe I have encountered the same problem as you and I believe this is an issue with the software. From your screenshot above, your pre-boil volume is 23 litres and your post-boil volume is 19 litres indicating a 4 liter boil-off. You then specify your batch size as 18 litres (fermenter...

Did you ever find a solution to this? I'm after the same thing. Liquid in the HERMS coil and under the false bottom is not in contact with the grain and therefore must be added to the strike water in order to maintain the proper grain to grist ratio.