They may have tampered with the groups recently so we really need to ask someone who flown as sapphire lately. I think I saw a Gold BP recently and it was in group 2 but I am really not sure about that.
Previously the boarding order was:
Pre-boarding (those in need of assistance, UM, anyone who can produce a child)
Group 1: Business class, AY plat, AY Gold, AY silver, OW E, OW S
Group 2: ?
Group3: Statusless Y-travllers, Finnair juniors
And as OP is flying ex-HEL, boarding groups may or may not be enforced. It may just be a PA call sayng "We start boarding now..." and may the strongest win.