Did not understand what's your point. So I'll give an example. In our guild to level an arc from 55 to 56 you need to donate 3021 FPs. 1st is locked by 1.85 boost to be 1656 FPs giving a profit of 44 for an arc with 1.9 boost, 2nd with 1.85 is locked by 833 FPs giving a profit of 22 for an arc with 1.9. Samewise 3rd is locked by 277 FPs with a profit of 8. That leaves only 4th & 5th to be in less than 255 FPs (3021 - 1656 - 833 - 277 = 255). To lock 4th you need to donate 128 FPs with a loss of 54 (128 - 40 (reward) - 34 (contribution reward for 1.85 arc boost) = 54). Then 5th is locked by 64 FPs with a loss of 45 (64 - 19 = 45). The rest of FPs left (63) are covered by the owner to level the arc. So as you understand 1st, 2nd & 3rd make a profit, which is good for them. While locking 4th & 5th comes at a loss to the ones that donated. The donors then inform the owner of the arc where they want their losses to be paid (let's say 54 on donor's A CoA & 45 on donor's B LoA), so it is a win-win situation for all of them as the owner can level arc faster, 1-3 get profit & 4-5 get FPs on the GBs of their choice that makes them closer to leveling their respective GBs. Additionally the owner of the arc can win rewards from donors A's or B's GBs by placing at a position (1 to 5) there.
I took quite a big of an arc boost (1.85) of the donors, but imagine if it is much lower then the loss to be repaid is much higher for 4th, 5th, sometimes 3rd and at a low levels for 1st and 2nd.