For me, the issue is non-intuitive EPR values. For example, on the GE90-115, full thrust is 100-105% over a large range of altitudes and temperatures. If you’re on a derate, <85% probably means something is wrong. In the circuit, F5, 55% and 5degs NU is a good starting point.
With EPR on the RR Trent, who knows? 1.372, 1.594, 1.193...? It’s not very memorable and changes much more with environmental conditions. Is 1.228 a good thrust setting for a derate? Gross error checking isn’t as easy.
At the end of the day, the AT doesn’t care if the units are nano furlongs per ounce second squared or walnuts per light year: if it’s slow it adds a bit and if it’s fast, it takes some away.
