In my opinion, do not force sorting by height. People are supposed to have fun during the photo. People choose a place next to a friend or a group of friends, next to the crush; probably they arrived earlier to be at the center.

Focusing on comparing heights will be chaos... ChAoSs.

You can define some categories tho. Women at the bottom and men at the top? Especially if they are sitting on a bench. The directive board at the bottom? First graders?

You need to focus on 180 people! ...really, you need to worry about more important things than height.

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Give clear instructions. Carry a megaphone. Start filling from the center to the edges to maximize a general composition.

Have two assistants, one for the left and one for the right, but only for implementing your centralized instructions; make them wear perhaps a colorful vest, so the instructions they give have a bit of authority.

Solve any technical stuff before organizing people. An assistant should solve any minor incident that presents, not you. Only focus on giving instructions.

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One thing that could be height-related is if the angle to the camera is too narrow because you are using a short focal length (A), then some short people on the back (4), could be covered by another (3). You could ask for the taller men to be in the far row.

(A few could get a box... LotR reference)

You could consider a longer focal length (B) or position the camera at a higher position (C).

Steven Kersting's advice of taking several shoots is a must. One instruction that you can give is that people stand comfortably but do not move their bodies at a given moment. Changes in the face and expressions are inevitable.

The other general advice is that the odd rows align to the middle of the even rows and vice-versa. So the faces will be in the gap of the two people in front of them.

Try to find the perfect, and I mean the perfect spot for the camera. The perpendicular line that forms with the stairs needs to be the center, if not, you will have parallelism problems, for example, people start looking smaller on the left vs the right, or the supposed horizontal lines could end up being convergent, and therefore inclined.

P.S. If you do not need to use the 6 steps, and the composition is good enough on, let's say 5, go for it. In my opinion odd numbers, 5 rows is better than 6, but if your categories need it, for example, it is a graduation ceremony of even numbers of women and men, 6 is ok.