Greg,
I seldom if at all see Jackie utilizing a mirage shield in formal competition all though they are quite common in the Gulf Coast region. I'm almost certain a shield was not used in his record agg at Midland. Maybe Jackie could chime in and shead some light on this matter.
If you look closely at the photo you'll see that Jackie has a March 10x60 variable mounted to his HV to combat heavy mirage.
Not that it matters but I've been competiting for 3+ years and have never used a mirage shield as of yet.