Internally I suspect the BC uses 16 bit numbers, but with midi it uses 14bit values and exposes them with val7.13 and val0.6 (or just val)
eg
$encoder 1
.minmax 0 $3FFF
.tx $F0 $42 $10 $10 $12 00 00 00 00 val7.13 val0.6 cks-1 5 $F7
Fictitious Roland sysex
If the binary value is
0011 1111 1100 0000
val7.13 = 0111 1111
val0.6 = 0100 0000
All the best
Royce