As far as I know, a TTS system that is savvy in imperial distances should probably read out distances of less than a mile as follows:
1 or more miles = # of miles
0.5 = half a mile
0.2-0.3 = quarter of a mile
0.1 or less = # of feet, starting with 500 (0.1 miles = 528 ft; the 28 ft over 500 is really insignificant on the road when approaching a turn) and counting down.
Typically, highways signs, at least here in New Jersey - and this is most evident on construction signs, starting counting down feet at 1500, suggesting that really anything less than a quarter mile should just be measured in feet. I realize 1500 ft is a little more than a quarter mile, but I guess it's more obvious and concise - and probably easier to print - on a sign than a quarter mile.
Something is definitely funky with the distances to roadside alert pins. I don't think it's showing metric figures instead of imperial, because that would make things appear on the Waze map closer than they really are. Rather the effect is opposite; I drive about half a mile and it only counted off a couple hundred feet.