Hi Gareth,

Search for 'rudder pitch coupling'
Here is an old thread of me:
http://www.rcuniverse.com/forum/m_15...tm.htm#1553776

The photo's got lost but it was a shoulderwing configuration with the stab placed low in the fuselage. It piched up strong. Placing the stab a bit above the wing position cured the problem.

To find the optimal position is a matter of trial and error. If you do not like to go that route have a look at the position of the elements in an existing design.