personally, i wouldn't do it at that size.

i house several of my adults together (arcifera, campbelli, nelsoni, sinaloae) and have for years without incident.

although typically they're adults/subadults when introduced for the first time and not put together until brumation time. the assumption there is, it gives them time to adjust to having a cage mate they can't utilize as a food source (lack of heat for digestion).

i've only been doing this for four years, and i do separate for feeding, but no issues so far.

just my two cents.
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i work with tri-colored west mexican lampropeltis. some morph, some hobby, and some locale.

everyone is entitled to their options, but no one's opinion will ever change how i feel about the snakes i keep and breed.