I don't know.  You may want to see if you have tongue ties or what-not.  I just think it's hard to retrain tongues.  If your face isn't broken, I wouldn't fix it.  Mine wasn't... and following some stuff about this kind of got my teeth messed up with curve of spee.  That was from applying pressure, though.  Applying pressure is not good.

Keeping teeth slightly apart in a comfotable position is good from what I read.  That is something I disagree with in relation to this site's article and Dr. Mew.  See my article about Bill Hang.  Anyway... sorry that I'm not much help.  I'm curious about some of the tongue exercises out there (outside of placement).  I think that it's kind of like exercising.  If you want awesome calves... you can try and hold your calf muscles tight for a while.   Perhaps, though, some dedicated time spent running some stairs every now and again would be a more natural approach.  It wouldn't create a habit that may possibly need to be stopped at some future date.  Those are my 2 cents, for what it's worth.  :-)