On paper, the derivation was 4 expressions and two lines of text. The Physics Derivation Graph yields a cumbersome 7 expressions and a total of 25 nodes (feeds, expressions, and inference rules).
Current output from the Physics Derivation
The reason the graph is large is because the "subXforY" is used three times. Analysis of the midpoint is really three concurrent substitutions: at y=y_mid, v_horizontal=0 and t=t_midpoint. Concurrent substitutions are not supported, so three steps are required.