[Harp-L] overblow question

[Pablo Basso <soplete@xxxxxxxxxxxx>]

Now i´m practicing the OB´s on a Bb Harp. I can play the 4,5 and 6 
clearly, but 1 overblow is very hard due the difficult to choke the 
upper reed. I gapped it very close (too much i think) but the reed still 
sounding.
what is the position of the tongue (more or less) to make de 1 OB sound?
I must gap both reeds (blow and draw) or only the reed to choke?

Thanks for your help.

Pablo.