Pre-Boil volume is 1.5 ish gallons lower than est. pre boil volume.

[Schwooby]

Which value/where do I change to make up for that?

I use a two vessel system that has 2 different 20 gallon kettles and 2 riptide pumps. I do 10 gallon, all grain batches.

I've set the dead space correctly in the software. Is there something else I should change?

[BOB357]

Sounds like you need to set up an equipment profile. Just accounting for dead space won't cut it. Here's a video from Brulosophy that will guide you through the process.
https://www.youtube.com/watch?v=QmW7pwQP5mQ

[Schwooby]

Sounds like you need to set up an equipment profile. Just accounting for dead space won't cut it. Here's a video from Brulosophy that will guide you through the process.
https://www.youtube.com/watch?v=QmW7pwQP5mQ

Thanks for the info, but that doesn't really address my issue.

[Oginme]

Actually, it answers your issue as best as possible with the scant data provided.  Did you accurately measure your water input? Grain weight? Do you no sparge, batch sparge, fly sparge? How did you determine your dead space?  What is your grain absorption?

GIGO.

Additional thoughts: There are two figures for dead space, one is recoverable dead space -- that fluid which will end up in the kettle after draining and the other is unrecoverable -- that fluid which will remain behind in the mash tun after draining.  Make sure you have your figures in the correct classification.

[dtapke]

Oginme forgot to ask, Do you BIAB?

Without knowing any specifics of your setup and method, it's impossible to tell you how to fix it.

the only answer that we could provide would be to add 1.5 gallons to your sparge volume, DUH!

[Kevin58]

You are not likely to get accurate results from the software unless you set up a custom profile by taking actual measurements. You may find a system just like yours in the list of default equipment profiles but you should only use that as a starting point for customizing it to your system.

Here is a tutorial which should help....

https://youtu.be/HwEbjOt8OR8