Hi Sakke
Maybe you are trying to push'pull the belly a little to hard.
On the inhale pull in gently, just a little,on the exhale
out just a little. Do not force it.
Also try breathing in and out through your skin,if you
don't do that already, may help.
Maybe not the words of wisdom you were looking for, but maybe
it will help.
Have a wonderful day
Gabby