To elaborate, that activity pattern (a 66 XP per direction round trip, which would not quite get BA Silver, each year), starting from Silver with zero XP would get you Flying Blue Gold 2 years out of every 5 (FB Silver the other 3 years) with no other activity and 5 years of BA Bronze (I think that's the sub-Silver tier over there?) out of 5.
Year 1: start with zero, add 132 XP, requalify as Silver
Year 2: roll over 32 XP, add 132 XP, requalify as Silver
Year 3: roll over 64 XP, add 132 XP, move up to Gold
Year 4: roll over 16 XP, add 132 XP, move down to Silver
Year 5: roll over 48 XP, add 132 XP, move up to Gold
Year 6: start with zero, add 132 XP, move down to Silver
(You're now in the exact same state you were in at the start of Year 2: Silver rolling over 32 XP)
The rollover almost certainly decreases the elite credit relative to status requirements in FB relative to other programs, but if you're able to consistently maintain any status, it actually becomes more rewarding longer term.