That’s why I said “depending on what your gear ratio is,” and, yes, some trainers’ load generators do have difficulty at extremes of wheel rotation speed. In ergo mode, a load generator has to produce the requisite resistance no matter how fast the rear “wheel” (or hub, in direct drive trainers) is turning, so it produces low resistance at high rotational speed and high resistance at low rotational speed. Obviously, trainers have a cut-off at low speed where they don’t add resistance or else you’d never be able to get started – at zero rotations, the resistance would have to be infinite – and I’m pretty sure it’s not on your trainer.
So, as it turns out, I know this because I ran across a friend’s trainer that did have a load generator that only worked in a narrow range of speed. My friend would set the “ergo” function and then pedal away, and he would be happily spinning away at high rpm because it was so much easier. This was a wheel-on trainer, not direct drive, so eventually I brought over my Power Tap wheel and it was obvious that his load generator was overmatched at high speed and couldn’t produce enough of a load to keep the power constant. Interestingly, in “slope” mode (as opposed to ergo mode) where his trainer was just measuring power rather than trying to control it, it worked okay. But he wanted to use it in ergo mode, so he exchanged it.