Single-wound coil flippers issue

[Dan]

Hi all,
I finally got my first benchtop setup running with just two flippers and one pop bumper :-P
It kind of works, but I cannot get my flippers to hold their position.
I have tried multiple guides and examples, and various combinations of pulse, power and hold-power settings, but with no much luck.
If I press and hold the flipper button long enough, I see that it kicks and then I can hear the coil start buzzing but after the initial kick the flipper drops back down and only buzzes.
I am using pre-assembled Stern flippers with a 090-5030-ND single-wound coil.
Is there a way to make this work?
My current config:

coils:
  c_flipper_left:
    number: 1616-0
    allow_enable: true
    default_pulse_ms: 28
    default_pulse_power: 1.0
    default_hold_power: 0.125

Thank you.