I think the astrological symbolism is better viewed within the context of traditional astrology (dignities, rulerships, qualities, triplicities, etc.,), seasonal allegories (N. Hemisphere), biblical references and classical myths or renaissance interpretations thereof than modern day Linda Goodman style 'sun signs'!?
The fiery furnace "was nothing else than an emblem of that region of the great circle which the sun enters at midsummer, or the sign Cancer.“
It is that part of the year (N.Hemisphere) when the sun makes "our greatest heats, longest days, and Summer Solstice."
The fiery furnace is also symbolized by the desert, where in St.John the Baptist (whose festival is connected with the Cancer solstice) cried out:
“"Clear the way for the LORD in the wilderness; Make smooth in the desert a highway for our God.”
Echoing the Prophet Isaiah:
35:8 "And an highway shall be there, and a way, and it shall be called The way of holiness; the unclean shall not pass over it; but it shall be for those: the wayfaring men, though fools, shall not err therein.”
Cancer is ruled by the moon, whose Chariot (Homer/Ovid) is drawn by two horses, one black one white, the reason being (Bassus, Germanica) that she is sometimes seen by night, and sometimes by day.
The chariot, in contrast to the other sitting, standing, kneeling or walking figures, may also be emblematic of the Moon (ruler of Cancer), the swiftest of the (astrological) planets.
...And why the nimble Moon
Does drive her Chariot faster than the Sun;
And in one Month thro all the Zodiack go,
While the grave Sun's a year in walking thro’:
De Natura, Lucretius, Book V.