Topic: High d on contra

I can't seem to get a high d on my contra (above middle c). I have tried Cornelia Biggers fingering and get the high g harmonic above the d (which actually sounds pretty good) but not a good d. If I use both the C # and the first (c) octave key I can at times get somewhat of a d.
Any thoughts or recommendations would be appreciated.
I play a Fox contra with a Heckel 3 bocal.
I also have a couple of Fox and a couple of Amati (unmarked) bocals.
I make my reeds from cane I get from Bob Williams - I really like the cane.
Brian Peterson