[Runequest] Shield skill penalty query

[royce at efn.org]

Greetings, Comrades,
   A question regarding shields in castles.  I have often been told that,
in the later medieval castles, the stairs circled clockwise so as to
put the invader (i.e., the fellow fighting his way upstairs) at a
disadvantage.  The idea being that, assuming the attacker to be
right-handed, it would be difficult for him to make effective use of
his shield.
   Is this story true?  And, if so, what penalty should it be in RQ3?
   Feedback is warmly welcome.
   Sincerely,
Asher