About 8 years ago I took an OSHA safety course lead by 2 OSHA inspectors in my region. I asked this exact question, but it was phrased in terms of stacking commercially available storage cabinets. We had a short cabinet stacked on top of a full size cabinet. The cabinet manufacturer advertised it that way.

One inspector, who happened to be taller than me, said that he allowed 1 short storage cabinet to be stacked on top of 1 full size cabinet (what we had). However, they had to be properly installed and we could only store small bottles (1L bottles or less) on the top one.

The other inspector, who happened to be shorter than me, was a bit concerned with her colleague’s answer. She proceeded to say that staking a short cabinet one on top of a full size one ends up being too high. She only allowed stacking of two or three short cabinets such that the height of the stack wasn’t much different from a full size cabinet.

It quickly became evident that eye level was the inspector’s eye level. After discussing amongst themselves for a few minutes, they both agreed that you shouldn’t go much higher than a commercial full size cabinet regardless of the configuration. They also agreed on a pecking order for stacking cabinets of different hazards, which evades my memory at the moment.

Truth be told, at 5’5” I could only reach the front half of the cabinet that was stacked on top. To reach bottles on the back half, I had to use a stepstool. In retrospect, storing glass bottles at that height was just a bad idea. Even if they were small.