The basic EIC works on a "bell curve," rising as a worker's wages rise reaching a maximum when annual earnings are between $14,800 and $19,350 (Single with 2 or 3 children 2020) and then declining gradually until it phases out altogether.
If your income is on the up slope of the EIC curve more earned income will increase your EIC. For those people having less income in 2020 also results in less EIC. This provision will help them.
But if your income is on the down slope, more income (of any kind) will reduce you EIC. So you would not want to use the 2019 option.
See the curve (graph) at:
http://www.taxpolicycenter.org/briefing-book/key-elements/family/eitc.cfm
