Update.
Well after a good number of useful responses to my query on the Outpost forum, I have received no direct reply as to what files outpost accesses on boot or why -
What files does outpost access/check at startup and why? I have an open support ticket about it awaiting a detailed (rather than automated reply) response.
I tried a number of things which had a limited or no effect at all.
Exclusions didn't work at all.
Disabling a number of other startup entries (SnagIt, etc.) very limited effect, confirming outpost was the cause of the excessive file activity and scans.
I also tried reducing the Standard Shield sensitivity to Normal from High (before disabling outpost), this had the desired effect reducing the scanned total from 800+ to 300. But I felt that this lowering of my AV defence wasn't acceptable.
It was only when outpost startup entry was disabled and the outpost firewall service was set to manual that there was a real effect, the scanned total dropped from 800+ to around 300.
Warning - It is important to ensure you start your firewall before you connect to the internet, so this may not be an option for those with a direct always on connection, for me on dial-up there is less of a problem.
Starting both the outpost firewall service and the outpost GUI manually was a bit of a pain and you have to do it in firewall service, GUI order. Fortunately someone on the outpost forum told me the run command to start the service
net start "outpost firewall service" (with the quotes because of the spaces). So I created a small batch file 'OupostStart.bat' located in C:\ with a shortcut in the quick launch tool bar (to give one click outpost start).
The batch file had the line to start the service and the path to execute outpost.exe, which started the GUI:
Net Start "outpost firewall service"
"C:\Program Files\Agnitum\Outpost Firewall\outpost.exe"