A good gauge is the power meter on the display. If I am on an economy run I try to keep it as low as possible for as long as possible. I do this by either backing off and riding slower in a lower gear but the best method is to pedal hard and go faster to push past the cuttoff.You never stated your speed, but given your in tour I'll guess 15-16mph. Try dropping it back around 12mph and keep it in eco, should be good for over 50miles on gentle terrain.
Faster you go more power is needed.
Strangely and depending on terain I have used turbo to good effect as it allows me to rocket up the the cuttoff and stay above it much easier.
I Think my best ever economy runs were 35 miles and 3000+ feet and also 60 road miles with no hills on a Bosch classic with the 400w battery. I can't match that on the performance cx.. but I am now 6 years older.