Let's look at it again.
(E) Raceway Supported Enclosure, Without Devices,
Luminaires, or Lampholders. An enclosure that does not
contain a device(s) other than splicing devices or support a
luminaire(s), lampholder, or other equipment and is supported
by entering raceways shall not exceed 1650 cm3
(100 in.3) in size. It shall have threaded entries or have
hubs identified for the purpose. It shall be supported by two
or more conduits threaded wrenchtight into the enclosure or
hubs. Each conduit shall be secured within 900 mm (3 ft) of
the enclosure, or within 450 mm (18 in.) of the enclosure if
all conduit entries are on the same side.
The base article does not say "conduit body" at all so there is no "size" defined beyond "<100 cu/in".
This means it could be a Bell box if that was what you wanted to use and you could still support at it 3" from both sides or 18" if both conduits come from the same side.
It is when you get down to the exception for conduit bodies that the conduit size comes in.
Exception: The following wiring methods shall be permitted
to support a conduit body of any size, including a conduit
body constructed with only one conduit entry, if the
trade size of the conduit body is not larger than the largest
trade size of the conduit or tubing:
(1) Intermediate metal conduit, Type IMC
(2) Rigid metal conduit, Type RMC
(3) Rigid polyvinyl chloride conduit, Type PVC
(4) Reinforced thermosetting resin conduit, Type RTRC
(5) Electrical metallic tubing, Type EMT