on a tablet, we don't want to use IE in Desktop mode.
Then you can just immediately use the Desktop's right-click Open in Immersive browser. No split screen then. Otherwise, if it is the extra swipe that bothers you, you can always do an Alt-Space M (M for Maximize mnemonic value instead of x for its compatibility with existing keystroke sequences which provide the same function.) I'm sure all these use-cases have been very carefully thought out... ; }
Tablet = no mouse for right clicking, no keyboard for Alt-Space M.
Right now the extra swipe is the only viable workaround, but as has been previously mentioned, the split-screen feature is neither desirable nor useful on a tablet and most of us tablet users would like to be able to eliminate the "feature".