Based on your info, I'm going to take a guess that during the pig rich light cruise, the throttle is barely cracked open; maybe 1 - 2%?

If not, stop reading now.

If so, you're cruising on the transfer slots, and most likely the main circuit hasn't started working yet; certainly not enough to do much good. As others have said, you can pinch down the transition circuit with t-slot restrictors and such, but before the problem is fixed, you'll create an off-idle lean spot. As others have said, you can help somewhat by reducing the size of the IFR, but again you'll probably lean out the idle circuit too much before the rich cruise is fixed.

Think about the 1-2% throttle position opening, and how that relates to the t-slots. At cruise (the rich spot) you have 12 - 14" hg sucking fuel through the slots, via the IFR. But when pulling away from a stop at the same 1 - 2% throttle opening, you probably have the equivalent of idle vacuum (7 - 8" hg) or less. Orfices that are sized properly for 7 - 8" hg are too big at 12 - 14" hg. So, when you pinch it down so it's "right" at cruise, it'll be too lean off idle at low vacuum.

The idle circuit (including the t-slots) works on manifold vacuum, not venturi airflow. Driving on the t-slots will always be a compromise bacause of this.

This is a very common problem with big Holleys and Holley clones on crisp-running engines that require tiny throttle openings to move them down the road.

Sometimes, ignorance (not having an O2 meter) is bliss, huh?

J