I do see where you are coming from, but in my opinion these snares are utility abilities that cover a core mechanic of the game: immobilizing vehicles. They should work reliably. The difference of doing 20 damage more or less is virtually invisible, the (double) snare still works if they bounce in basically all other occasions except for what basically boils down to the Brummbar and Comet (so the player fully expects a vehicle to be snared), but yet if it does not work the game is just perceived as buggy. None of these differences are noted down anywhere, and from a gameplay POV they don't make much sense either.
Overall it is a rather minor issue though, but still an issue.
I agree with the bottom points.
To me the rule should be the same vehicles will get engine damage under 75% HP and die at 0 HP, but that irrelevant to deflection damage and penetration values.