Estimates for undetectable planets in extra-solar systems
Based on answers and comments on some previous questions (especially this one), and as very clearly illustrated by the scatter-plot here, there are some very definite limitations on our ability to detect exo-planets that are below certain sizes or beyond certain distances from their stars.
From what I've been able to determine, it seems that Uranus and Neptune are about as small as we can detect unless the planet is relatively close to its star, And Earth is near the lower size limit we can detect, regardless of proximity to the star.
In other words, our bias toward detecting large planets, and planets close to their stars, means we have reasonably good data regarding how many of those kinds of planets are generally present in a system, but we can't tell (by direct observation) how many small planets are generally present in a system, or how many planets are present that are just too far from their star for us to detect.
My specific question: Are there reasonable scientific research data, models, estimates, theories, evidence, etc., that describe the likelihood of these "undetectable" (or very hard to detect) planets being present in a planetary system?
For example: our system has 8 planets, 4 rocky, 2 gas giants, 2 ice giants. But chances are that if we were observing (with current technology) our own Solar system from some other solar system, we'd probably only see 2 to 6 of them. We'd almost certainly see Jupiter and Saturn, and we'd almost certainly NOT see Mercury or Mars (they're just too small), Venus and Earth "might be" close enough to the sun for us to see them even though they are on the small end of what we can detect, and Uranus and Neptune also "might be" detectable, even though they are small-ish for their distance from the sun.
Is our system considered to be a "normal" planetary system, by the standards of current known science? What does science predict that we 'would' find, if we 'could' detect all planets around all stars? What does science predict to be the 'average' number of each type of planet in a random planetary system? Are gas giants really more abundant? Or does it only seem that way cause they're easier to see? Is our 4 rocks and 4 giants, a 50-50 split, normal? Or do we expect to find double the rocks for each giant in most systems (or vice versa)? Is 8 planets on the high end of the predicted spectrum, the low end, somewhere in between?
There are similar questions here on SE, but I haven't found any that provide the information I need:
https://worldbuilding.stackexchange.com/questions/21408/creating-a-realistic-worlds-map-planetary-systems
https://worldbuilding.stackexchange.com/questions/116102/ive-determined-how-many-planets-my-solar-system-could-plausibly-have-how-do-i
https://worldbuilding.stackexchange.com/questions/116059/how-many-planets-should-i-have-in-my-planetary-system 710