Both a diagonal and a impulse are a motive phase, so a rule is almost the same, but a wave 4 of the diagonal could overlap with its wave 1. It is also not suprised wave 3 of diagonal is the highest. In this case, wave 5 is failed and the link provides the explanation.
tradingview.com/chart/EURUSD/paAbs4wA-Impulsive-Corrective-Breaks-How-To-Identify-Trade-Them/