ORIGINAL: w8ye
I change it by trial and error a little at a time
I had a LT 40 back when they first came out that obviously had too much incidence for the amount of power that I had. I kept shimming the rear of the wing until I was happy.
The LT 40 has a flat stab. The Telemaster has a lifting stab which is supposed to negate the positive incidence on the wing but it doesn't completely do the job.
One good way to judge your trial and error is to watch the apparent attitude of the plane at your normal flight speed. You want the fuselage to appear level. You can adjust wing, stab, and engine thrust to achieve this.
I have already followed your suggestion on an LT40 I had on the shelf. I added about a quarter inch to the rear. I also swapped the OS 40 two stroke with an OS52 four stroke. I'm taking it with me on my next trip to the field to see how it worked out.. I should know in about two weeks.
That plane always had a rather odd look about it as it passed over the field. Tail down attitude, more or less. The beast is so beat up I'll probably retire it soon and strip the equipment.