When adjusting swr on this loop, a very little change will make a big difference. Mark positions of shorting bar and gamma match outer tube before moving.
If you need to adjust loop for a lower swr, start by loosening both set screws on the gamma match shorting bar. Movie the gamma match outer tube closer or farther away from the SO-239 connector. If more adjustment is needed, move the gamma match shorting bar closer or farther away from the SO-239 connector.
A combination of both will yeild a flat swr at your desired frequency.
Retighten set screws when done.
Measurments shown are a starting point only.