For anyone who is interested here are some 136kHz EWE/Flag dimensions from
Floyd Koontz

The top wire is 15ft above ground and the bottom wire is 5ft above ground
the lengths 100ft - 350ft are for the top and bottom wires

Rf is feedpoint impedance and Rt is termination resistor

100ft   -66dbi,  f/b 38db   Rf =1136,  Rt=1139
150ft   -63dbi,  f/b 31db   Rf=1128,   Rt=1142
200ft   -60dbi   f/b=30db  Rf=1124    Rt=1146
250ft   -55dbi,  f/b=35db  Rf=518      Rt=522
300ft   -54dbi   f/b=40db  Rf=512      Rt=522
350ft   -53dbi   f/b=21db  Rf=445      Rt=460

Looks like 250-300 ft a good choice and a good match at 450 ohms

73s Tracey