This setting --avalon8-voltage-level-offset has no effect on mining speed so I set --avalon8-voltage-level +3 with results and it loos like +5 is the default setting.
around a 1000GHs drop and a slight temperature drop.
13204.45
30/70
13447.80
29/74
13630.70
29/74
GHSav
39591.71
I'm not sure you are seeing what you think you are... the value range that the controller works with is -2 to +1, a +3 or +5 will return an error and either default to 0 or not start.