It depends......on the classificiation of the reflector.

For cyclically (non-tubular) use AWS D1.1:2010 Table 6.3, and take note of the classifications at the bottom left of page 241.

A is rejectable regardless of length
B is rejectable if longer than 3/4"
C is rejectable if longer than 2" in the middle half of the thickness, or anything longer than 3/4" in the top or bottom quarter of the thickness.
D is acceptable regardless of length or location