Flash content too small under IE

Drupal 4.7.2
MySQL 5.0.18 / 5.0.1.6 client
PHP 4.4.2

The Flash filter is working beautifully under Firefox, but I can't get it to display properly under IE, where it appears at less than half the size. In Firefox it displays at the correct 438x336, in IE at a dwarfed 192x149.

My Flash filtersettings:

'node teaser max' set to 800,600
'node body max' set to 800,600
'Try to display inline via tag' selected
'At the very end of a teaser part' selected
'At the very end of a node body part' selected
SWLIVECONNECT unchecked
PLAY checked
LOOP checked
MENU checked
Quality set to 'best'
Scale property set to 'showall'
Window Mode property set to 'window'

My code for the Flash content itself:

<OBJECT classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000">
<PARAM NAME=movie VALUE="files/MyFlashFile.swf"> 
<PARAM NAME=quality VALUE=high>
<PARAM NAME=bgcolor VALUE=#FFFFFF>
<EMBED src="files/MyFlashFile.swf" quality=high bgcolor=#FFFFFF WIDTH="438" HEIGHT="336" >
</EMBED>
</OBJECT>