I think your intuition is leading you the wrong way (I'm not a statistics expert either, so happens to me quite often as well; no offense meant )
To me, the best way to think about it is by enumerating all possibilities. If you flip one coin, you have 2 possible outcomes, each with probability 1/2.
If you throw 2 coins, you have 4 different combinations: (heads, heads), (heads, tails), (tails, heads), (tails, tails), all with probabilty 1/4. So, your chance on having at least one succesful result (let's say heads) is not 1/2 but 3/4. Replace (heads, tails) by (immobilized, not immobilized) and flip the coin many times, and you'll feel that the chance at getting immobilized is way higher than the original 1/2.
Lotto is something different altogether: the chance of getting the correct 6 numbers (out of 42 balls) is something like (6/42)*(5/41)*(4/40)*(3/39)*(2/38)*(1/37)=0.00000019 and something. Conclusion: don't play lotto, it is made to take away your money
This leaves the question: if the immo check is done per element tile, immo probabilities will be significant, even for small distances travelled... even just an hour ago, my opponent again experienced the same thing: 4 vehicles immobilized in one battle (Elsenborn), one by a tree, 3 by Leaves & Brush (no kidding). Really bizarre...