I'd guess that EDS tokens are being minted faster than your minting
your EDS tokens if that makes sense. EDS mintage each week from both EDS miners is 300, which was for a very long time. We added @eds-vote 6-7 months ago and it mints around 100 EDS per week and now we've have EDSD minting another 40 EDS per week. So we could say that the weekly EDS mintage has increased by 45-50% over the past 6-7 months.
This does dilute HIVE income payments per EDS token but this should not be a surprise because the EDS APY has been dropping for over a year now and I highlight it every week.
My guess would be since @eds-vote came along, more EDS have been minted and the ones that you are minting have less of an impact and is resulting in less share of the total income pool.