A beersmith/mash tun question

So i started using Beersmith recently and am constantly struggling with the amount of water to use in mashing and sparging. Im using a 10 gallon home depot round cooler and a bazooka tube. Not sure if lauter tun deadspace is negligable because the grains are resting on the bottom. Also does anyone brew in Arizona because it seems my boil off is CRAZY. Around 20% evap rate is my calculation!? Thats on a bayou turkey fryer uncovered outside. Does this seem right at all???

I did a loss test with my 10 gallon rubbermaid cooler I just converted... Turns out I have a 2 quart loss on the bottom... I've already entered that into my equipment profile... You can make your own custom one, tweaking the settings so that you can get it right for you.

I set tun loss at zero but my tun sucks out almost everythign when testing with water. It leaves about 1/4 cup.

20% boil off is what I used to have when I used a pot. If you have a faily wide pot (if it's about as tall as it is wide) then 20% is probably right. After a couple of years of using the pot (it was a ten gallon megapot) I switched to a keggle. The keggle only boils off about 15-16%.

Theres nothing wrong with the 20% boiloff. You just have to plan and increase your pre-boil volume accordingly.

Thanks guys, good to know thats about right. Felt like what everyone else was talking about was so much less. Wasn't sure about my setup. I am using a 40 qt pot so sounds like I've been doing it right. Thanks again, I can always count on you guys!