Fresnel effect too dominant for IOR=1.5

Hello!

First of all thanks for the great free raytracer. I started with blender/yafray a few weeks ago and am very
impressed  what can be done with it.
But when trying to get a realistic wine glas with yafray and caustics I got stuck reducing the fresnel
effect. In the net I found a statement that it would be implicit linked to IOR. Comparing it with the blender
internal raytracer and physical values (5 and 1.25,
http://www-nw.uni-regensburg.de/~.grr06742.back.physik.uni-regensburg.de/BLENDER/GLAS_B~1.PNG)
it is obviously too dominant (freoff= 1.25:
http://www-nw.uni-regensburg.de/~.grr06742.back.physik.uni-regensburg.de/BLENDER/GLAS_B~2.PNG)
in yafray pics even if the fresnel offset is set to the maximum of 5 (freoff= 5.00: http://www-nw.uni-regensburg.de/~.grr06742.back.physik.uni-regensburg.de/BLENDER/GLAS_B~3.PNG).
I would like to know where the strength of the fresnel effect is set in the code of yafray or how to influence it
in the xml code (I couldn't find any docs on that and changing the fresnel offset to negativ values in the xml
file didn't help).

By the way: When disableing RayMirror in the Blender yafray settings the fresnel effect does not
disappear. It just seems to influence the shading ad the sides of the glas.
I'm using yafray 0.9 and blender 2.45.

Any help or hints apreciated
Lynx