>Do you

really use your upper canines and premolars to make the "th"
fricatives? Then they are probably slightly lateral (a bit like Welsh
<ll>), aren't they?

>
> Piotr

My tongue has always tended to stroke the upper side teeth when making
these fricatives. The tongue is spread wide at the front of the
mouth, resting just under the teeth, almost as if I was
going to 'scratch' my tongue with my upper teeth. I forget what Welsh
orthographic ll stands for; for some reason, my memory insists it
should be like the double L in llama, but this cannot be correct.