[mflaming]

Do you think it would be okay to alter the height of the XLS cabinet? This is just for cosmetic reasons. They seem a little squatty to me.  I’d like to add about an inch and a half to the height.

[Hobbsmeerkat]

The height is about the only thing you can modify without affecting the response. so adding an inch or two to that model isn't a problem,
(so long as nothing else changes)

[E-Zee]

I'll give a second vote, in agreement with Hobbs.  Keep the width the same. Keep the driver spacing the same.  Add some height. 

I've experienced increased height / decreased depth modifications on several designs without impact.  In a few cases that height adjustment was to accommodate a front slot port instead of a traditional rear port.   The baffle width,  and driver spacing should remain the same and your adding a little to height won't have detrimental effect. 

[Danny Richie]

Only add the height below the woofer though. Don't change the tweeters height to the top of the cabinet.

[mflaming]

Eight months later and I'm still thinking of building a slightly taller XLS, but also with a front port. I know some have built the towers with front port, but what about the monitors?
It would be the standard XLS but with a height increased from the standard 13.5 to around 15.5 with port in the lower corner.

I've built the standard monitor, and the tower and this may be my ideal compromise as long as a front port wouldn't somehow mess with bass response excessively. These would be placed back up against the wall on a AV cabinet, not ideal, but any speaker that I move out into the room will promptly be returned to wall by my lovely wife. Compromise. Along the same line, would a sealed monitor work? I have the GR/Rythmik sealed sub, so less bass response might be okay.