The easiest way I can explain it is to get your tongue to flutter with a steady stream of air without the call in your mouth. Blow as hard as you need to to attain the fluttering action of your tongue. Next place the call back in your mouth. Let the call "float", and apply just enough tongue pressure to keep it in place. Then produce that same stream of air to get your tongue to roll. You should make some type of sound that resembles a purr. Keep in mind to use as much air as you need to to get the initial tongue flutter. Then back the air flow down to make it real.

front note of the yelp- I pulled this from an earlier post where a gentlemen asked the same question.

This one of the hardest things to teach people. From a technical standpoint, to remove the rasp in front note of the yelp you have restrict or hinder the reeds from vibrating.

The easiest way I can explain it is as follows.  Lay your tongue flat on the call with light pressure.  Then push air from your diaphragm(not blow) over the call. Again envision your keeping the reeds from vibrating. Then as you start your yelp, drop your jaw.  This will allow the reeds to vibrate creating rasp.

Another helpful tip is to lay your tongue on the call flat and then push your tongue forward with the end of your tongue touching the back of your front teeth.  Do not drop your jaw and force air across the call.  You should be able to produce a clearer, cleaner sound.  Once you have mastered this, incorporate your jaw dropping or basically relieving any pressure on the call.  This will allow the call to create rasp.

To answer your question about bending the call, yes, it does tend to loosen the tension a bit on the call, but it should not affect the overall performance.  You may want to look into our small frame line of calls.  These  should fit your palette better...

S.E.