Pilotage,
Without seeing the whole of the Jep chart for the LTMA it's not possible to know if your (mis)interpretation was (in)correct (delete as appropriate
.
On the portion of the chart in your post, though, you can clearly see the "steps" - from East to West, there's the dashed blue line marking the edge of the Sfc-2500 CTR, then the purple line running N-S just W of Henley - WOD marking the edge of the 2500+ LTMA step, then the purple line on the 1 deg W line - which is marked on your Jep chart as 3500-FL245.
On my CAA chart, the 2500+ LTMA line isn't marked as such
at that location - however, it is marked clearly to the S and N of that area - right beside Wycombe Air Park, as a matter of fact
Is it possible that the "middle" line is noted
elsewhere on the Jep chart and that you have missed it?