In early January, 2019, our group from RIT discovered a small problem with taking dome flats: the dome did not always move to the correct position, so that the white circle was exactly in front of the telescope and the lamps mounted on it.
After several nights of experiments, we found that using ACE to the telescope and dome to "Dome Flat Park" position consistently left the white spot slightly too far to the right of the telescope's position. The dome azimuth of 74 degrees set in ACE for this "Dome Flat Park" wasn't quite right. We found that a value of 67 degrees for the dome azimuth was closer to directly in front of the telescope.
Judging the proper relative positions of the telescope and dome is not an easy task, especially in the cold for a sleep-deprived observer. We have tried to help by placing some markers to help others reach the proper position. These markers are pieces of masking tape, placed on the metal band attached to the rotating dome. As shown in photograph below, which was taken from the platform in the 0.9-m dome, facing the dome/floor motion panel, the masking tape will flank the fixed supports behind the dome/floor motion panel when the dome is in the proper position for flats.
As the tape will eventually lose adhesion and fall off the metal band, it would be wise to make some more permanent marks; perhaps bright paint might work well.