Can you explain more about the decoction method?
Decoction is the process of removing a portion of the mash, bringing it to a boil, and adding it back.
For some lagers the brewer will do this several times as they take the mash through various rests, I only do it once.
My method for a 5-6 gallon batch using 9-10 pounds of grain is to remove 1.5 - 1.75 gallons of mash once it passes an iodine test, bring it to a full boil, then add it back. This takes a mash of 145-150 and raises it to the neighborhood of 170. While this is going on I heat the sparge water and set up the equipment. Then I carry on as I did before.
This step adds a half hour or more to the process, and it had a dramatic increase in my efficiency.
The first time I did this I didn't take any pre-boil gravity readings and used my normal amounts of hops. The result was not at all what I intended.
If you do try this my word to the wise would be to use your pre-boil gravity (don't forget to adjust for temperature) and volume to calculate the gravity of what you will be fermenting, and adjust the hops accordingly.