I am printing with ninjaflex for the first time and getting my best results with an extrusion multiplier of 1.5 (after at least 20 failed attempts). Is that normal? My extrusion multiplier usually ranges from 1 to 0.96.
If your extruder drive gear really compresses the filament, the smaller effective diameter will result in less volume per turn, so some increase in extrusion multiplier can be expected.
Thanks for the very prompt response. It sounds like there is an intricate dance between idler tension vs extrusion multiplier. This could be a long weekend 
NinjaFlex is amazing stuff, but it’s very different from ABS or PLA. I find that I have to design parts differently to print with it. For example, thin vertical walls in NinjaFlex wobble during printing so much the print has holes everywhere, so I had to make them 2mm thick so they were stiff enough to print. And you have to go very slowly.