In Construct 2.10.69 the Hex() adapter uses the number of bits as number of bytes when formatting BitsInteger() fields, such as Nibble(). It should detect that it is used on a bitwise field and compute the number or nibbles (or bytes) from the number of bytes, rounded up towards the next full integer.

Minimal example:

from construct import *

d = BitStruct("a" / Hex(Nibble), "b" / Nibble)
print(d.parse(b"\x42"))

Result:

Container:
    a = 0x00000004
    b = 2

Expected result:

Container:
    a = 0x4   (or 0x04)
    b = 2