Here are some notes from my playthrough last year:
"Also, it seems to vary based on which version of the game you are playing, but in the SNES version of the game I am playing, the amount of experience your characters earn can vary depending on whether or not your characters are directly facing an enemy and/or whether they are attempting to perform the action from the back row. In the SNES version of the game, your characters definitely earn significantly more experience for performing an action from the action menu when they are directly facing the enemy from the front row than they would if they performed the same action from the back row or while facing away from the enemy. War Cry is a bit different, though - in the SNES version of the game, you seem to get the same amount of Fighter/Healer experience for using War Cry while facing the enemy from the back row as you do when facing the enemy from the front row; however, you gain less Fighter experience and no Healer experience at all for using War Cry while facing away from the enemy (even if the enemy is actively attacking your flank while you are performing your War Cry repetitions).
Also, despite the fact that my characters would earn significantly more Ninja experience per repetition by using "Stab" directly at screamers from the front row (my guess is twice as much), I have found that they can actually earn Ninja experience faster over time by performing Stab at the air or a wall while a screamer flanks my party from the side due to the sheer number of repetitions of the action you can perform from the character inventory menu (where the speed of time is approximately doubled). This method of gaining experience also benefits from the fact that you don't have to periodically clean up after dead screamers and temporarily leave the room to regenerate new ones. Finally, it can take a longer amount of time than you might think for a group of newly-generated screamers to actually attack your party, so you would also frequently lose the 2X multiplier for being attacked by an enemy within the past 4.17 seconds if you were earning experience by attacking/killing/regenerating the screamers instead of just attacking nothing while letting them flank you."
Some more general information on experience in Dungeon Master is available at ChristopheF's Dungeon Master Encyclopedia at the following links:
http://dmweb.free.fr/?q=node/692
http://dmweb.free.fr/?q=node/690
Bottom line, though, is that using "Stab" at a wall or the air while being flanked by a Screamer is the fastest way I was able to gain Ninja experience in the Screamer Room during my playthrough of Dungeon Master last year.
--Jay