There's a huge difference between1/72 and 1/87 (HO) scale that is very easy to pick out unless the viewer is kept at a good distance from the display. Assuming an average height of 1.8 m for a person, a 1/72 figure comes in at roughly 25mm tall and 1/87 makes the figure 20mm.
If you're going to use model railroad suppliers, I'd suggest OO scale, which is pretty close to 1/76, where figures are about 23.5 mm tall. This is close enough to suggest random differences in height and stature.