Im not entirely convinced that light-time is the culprit here. The Earths orbit is not circular, its elliptical, as the Earths orbital eccentricity is non-zero. Because of this, the Earths distance to the sun throughout the course of the year is not constant, and therefore the time delay due to lights finite speed will not be a constant either. If you have computed this value of 7.46988 to a high enough accuracy, there should be some variation throughout the course of the domain, a year. According to you, there is not.
Might I suggest a possible explanation? Its trivial. And if Im right, its a naive mistake. Are you taking into account your longitudinal offset from Greenwich (or from your time-zones defining longitudinal meridian)?
You said Right Ascension, so your location on the Earth should not be a variable, as Right Ascension is measured with respect to the stars. If you truly are measuring RA then Im at a loss for help and you can disregard my previous paragraph.
As I understand it, any body that passes through the Vernal equinox has a RA of zero. However, there is a distinction between mean and apparent vernal equinox. There are precessional and nutational factors involved.
Furthermore, one thing I am VERY fuzzy on, is whether or not we use the true vernal equinox at all, or if RA is based on the original vernal equinox defined thousands of years ago, known today as the First Point of Aries. They are well out of synch today.
These previous two paragraphs, if not taken into account, could cause significant errors that appear constant in the short term.