I think it's the variation in EPR ranges with environmental conditions on some engines that makes the number itself fairly useless.
RR Trent 895 max climb EPR ranges from 1.132 at a hot sea level to 1.518 at 43,000'. To fly level at 270kts, 15,000' and 160T GW you need 0.978... I can only quote these figures because I have the QRH displayed next to this posting. The numbers do not lend themselves to intuitive use, to put it mildly.
Comparing to something like the JT8 on the "classic" 737. 1.0EPR meant zero net thrust, 1.8-2.2 was full power. If you lost an engine on approach when you needed 1.3EPR on two, then 1.6 (twice the decimal part, plus one) would be a very good ballpark for the remaining motor. I can't remember now but there was another simple formula like taking 17 off the gross weight which would give you a very reasonable initial setting for a F30 3deg approach.
Point is, using N1 for a quick gross error check on takeoff, you're looking at c.85% on a full derate. Anything less than that should raise an eyebrow. Getting closer to MTOW, it's going to be into the 90's, probably 96-97% at the max.
Yes, of course you can get the books out and look up what kind of EPR to expect given various parameters but that sort of shows the lack of information from the original units used. Might as well be calibrated from blue1 to yellow15 with a limit of "sausage"... You get a power gauge on a Veyron (0-1001bhp!) and power reserve on a Rolls-Royce (100%-0), why can't we have a Thrust-o-Meter(TM) calibrated 0-100%?