file reputation/ prevalence is based on how often is the program in question being used by the majority of Avast user base.
if u run programs which are not commonly used by average users, be prepared to see many autosandboxing. it is done as such to protect users from potentially fresh malware (zero day)
however, it will also mean a huge increase in fp (in the sense that it sandboxes them) until the program is opened enough times by sufficient number of avast users for its behaviour to be analysed and tipping the overall analysis of the program that it is likely to be safe, thereby releasing it from be autosandboxed in the future.
there are 4 things u can do, either manually adding all programmes that triggered the autosandbox, or, run the program which triggers autosandbox and select ' open normally', or, set autosandbox to 'ask' so that programmes do not get sandboxed automatically, or, turn off autosandbox feature.
as far as i know, avast does not whitelist any programs which cause autosandbox to be triggered.
as for still prompting to run in sandbox inspite of adding to exclusions list, i cannot reproduce it on my side.
u might want to provide ur system specs, the program ur trying to exclude from autosandbox for avast developers to reproduce
meanwhile, do try a repair through avast uninstaller to see if that solves ur problem.
do note that during the weekends, avast team are generally not around on the forums, please be patient till next week.
edit 1: static analysis trigger is something u should take note...it is a more 'serious alert' compared to reputation trigger as this is based on heuristics
unless ur sure that the program is safe, do not release that program from sandbox.