Fixed staking income not fixed.

Hi all. I'm new on here but on Binance more than a year. And still learning. My issue is committing funds to fixed staking for 90 days at a high return. And then Binance changing to a lower return. In particular. I staked BSW. The advertised return was 143.25% during the promotional period, reducing to 100.23% at end of promo period. But now the return is dropped to 58.9% within the initial 90 day investment period. I have contacted support, and it seems that this is not a mistake but allowed for in the terms and conditions. It just doesn't seem right that if I am tied to a fixed term, that the interest can be so reduced.