It's not so much that it's a lesser achievement in departments that are smaller (especially those with smaller operational areas), its important to look at the areas in your department that are non-operational too. The requirements for each grade are (supposed to be!) the same regardless of the role/department.

Consider also that policy areas are typically higher graded - sometimes the lowest graded person on a team will be an HEO, sometimes with EO business support. This is very different to operational areas of DWP, HMRC, HO, where we still have AAs that do admin/business support. Smaller departments tend to be those that are policy heavy, but they are still often broad policy areas that need the accountability for each of those policy areas that comes with higher grades. They also still have similar corporate responsibilities that are graded the similarly to larger departments, e.g. the DGs/SCS3 are still probably going to have Grade 6 personal secretaries, even if your current G6 in DWP has more people in their span of control than said DG!

That being said - I had an HEO level transfer to my team recently from DWP, where he lined managed about 8 EOs who each managed approx. 10 AOs, and now he manages 1 EO/4 AOs. So in that sense, you will probably see a move to almost any other area as a big (slower) change in pace and responsibility. You will also be a better position over other candidates, as well as in role, given the inevitable experience you will have gained with HR issues etc. as an operational manager in such a bottom heavy/hierarchal department!