On a boat with an 8' beam with the engines in a side by side set up, mounting the tabs flat is usually not an option they will hit the drives. Many times the 380 plates in an angled set up will still have to be trimmed to clear the drives in a S X S application.

I'm re-rigging/restoring my twin O/B 24' Sonic and have the Keikhaefer tabs off. They were mounted on angle and I think they're going back level. Great point about interferance w/drives. That'd about ruin your day after all that work! Mine are angled on the inside to help this issue.
One thing w/my paticular rig is that it flys bow high and at speed, tabs mounted at angle would still be wetted surface even when pulled all the way up. Mounted level they would not and that is my main reason for changing them.
Interestingly, on my 1st 24' Sonic it had Bennett sport tabs which were fine for what they were. I only have a couple hrs in this boat before gutting it and the Keikhaefer tabs manipulate this boat WAY different than the little tabs! They are probably border line big for this hull and I felt like I wanted to slow the tab motors downs as they seemed to free wheel past the sweet spot. Will be interesting to compare w/them flat.
Great points to ponder. Thanks guys!