This goes to the issue of trimming philosophy. There are different ideas on how to setup a plane. This is how I do it. I start with CG @ 25% and on low rates.
1) Trim the plane to fly straight and level at full throttle
2) Move the CG aft until I get the amount of instability I want, usually around 30%. If you want a lot of stability keep CG at 25%.
3) Do the dive test.
Dive test: fly very high, cut the throttle and put the plane into a straight down dive. The goal is to be at to dive 150-200 feet straight down. If the plane quickly pulls out of the dive right side up, you need less down thrust. If the plane. If the plane pulls out bell side up, you need more down thrust.
Why it works, when you trim for straight and level at full throttle, you trim out any errors in thrust or incidents. When you dive without power, you remove the thrust and yet maintain good speed. This will allow you to see what was trimmed out.
How quickly the plane pulls out will give you an idea how much thrust angle change is needed. If your plane pulls out in less than 50 feet, you need a large change 4 degrees plus. If it pulls out in 75-100 feet, you’ll need 2-3 degrees. If the it pulls out is 100-150, 1 degree or less.
When you get it right the plane will fly well at any speed.