Certain areas in the Sector Maps require you to find a precise location around (or even in) the graphic representation of a nebula or planet before you get the 'Enter X Area' prompt, rather than just approaching within 1LY of said heavenly body. I spend more time trying to find the right spot to enter the Hromi Cluster than I do in any one assignment related to it (Diplomatic Investigation, Exploration, etc).
I've had the same issue at the Hromi cluster plus Arcunis arm. Had a laughing fit trying to get my old D'Deridex into these places. Half of the time I end up warping to the next sector, maybe it's due to the clusters being so close to the borders that the active spot is smaller. If so can the devs move them a little and make the active spot larger?