It is known that there exists a linear relationship between the maximum velocity of the prereversal enhancement (PRE) of the E × B drift and the strength of the equatorial ionization anomaly (EIA) crests at night. This can be a particularly useful relationship in the event that only one of the quantities is observed. But it is important to understand the drivers of the linear relationship in order to determine its range of validity. In this study, we use the SAMI2 model of the ionosphere together with measurements of vertical E × B drift velocity at Jicamarca to show that daytime drifts significantly affect the slope and linearity of the relationship. To validate the model, nighttime O I 135.6 nm radiances measured with the Tiny Ionospheric Photometer (TIP) aboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) are used in coincidence with the E × B drift measurements at Jicamarca. From the observations, we derive a linear relationship between the crest-to-trough ratio of the EIA NmF2 and the PRE under solar minimum conditions. The model simulations demonstrate that the influence of daytime drifts on the nighttime ionosphere varies with longitude and solar cycle conditions; and therefore the linear relationship also varies with these parameters. In particular, we show that the late afternoon drifts at solar minimum have the effect of steepening the slope of the linear relationship. On the other hand, the extended effect of daytime drifts under solar maximum conditions, including contributions from midmorning hours, tends to weaken the relationship.