The Republican Electoral College advantage is defined as the Republican nominee's percent margin in the tipping point state, minus their popular vote margin. So, for example, in 2020, Trump's margin in Wisconsin, the tipping point state, was -0.6% (a loss of .6%), but his margin in the popular vote was -4.4%, giving him an Electoral College advantage of 3.8%.

"No advantage" means the Republican advantage is negative or 0. The intervals are half-open in the form (lower,upper], though that will not matter except in the astronomically unlikely situation of the advantage being an exact whole percentage.