There’s a picture of Southgate’s notes in on field positions from the Mirror with the suggestion that Alli and Sterling miss out. When you look at the picture the whole squad is on his sheet for selection except Alli, who’s name is written in red as Ali with medical (I think) next to it.
Sterling is listed in the right forward midfield group along with Ruben (easier to write than Loftus-Cheek).
This plan is just grouping the players with what appear to be similar abilities/ preferred areas together.