It's non-negligible, but the reasons ultra-right parties like Otzma Yehudit [0] have a voice in politics has more to do with election calculus by Netanyahu.
The ideal 2+ party parliamentary system seems to be >2 but <6.
Below that, you get bad outcomes (US). Above that, you get bad outcomes (Israel, India).
Somewhere in the middle, it forces the right amount of coerced cooperation... most of the time (Germany).
You mean < 50% (strictly less than 50%) right? Otherwise the opposition would form a government