You are probably referring to the rule of 8. So 8:1 is a kind of rule of thumb people use. It works as a general guide but you might just have to hear itYep
I think there was some rule of like source impedance to be some percentage of the IEM impedance but I don't remember the exact value.
With almost 13 Ohm you could yet have an acceptable bass with around 1 Ohm or a bit higher whereas with my Andro Golds it's supposed to be at around 0,5 Ohm to have enough punch from my experience...
But others like @Rockwell75 have far more expensive with that I suppose...

For example, I loved the Cayin N6ii/A01 SE (OI=0.6ohm) with my Andro. I didn't like it so much with balanced out 1.2ohm, not to mention hiss that came with it. Out of Fiio M11, Cayin N6ii (all modules), DX228/9/8FE/8custom, and M8, M8 balanced/SE is my preferred pairing.