I didn't notice this game before, but I have to say I seriously doubt the situation is covered appropriately by the rules, which incidentally I can never even find on this site.
Personally, although I didn't think so a few years ago, I believe blocking rules in ropers need to be done away with, simply because there are too many situations like these where both sides aren't sure what to do. Any adequate definition of blocking, something that covers every situation, has to take at least a paragraph to explain, and that kind of convoluted rule isn't worth having when the alternative is just fine.
With blocking allowed, you could simply opt to play on maps with no blockable spots if you don't want to deal with blocking at all. And on maps with blockable spots, you'd just need to be extra careful where you hide; if you want to avoid getting a mine on your head by being up against a wall, you might pay the price and get blocked. The only situation that I used to be concerned about with blocking allowed was making a specially designed map where you could continually mine-block or ass-block (like a worm covering the exit of a very thin vertical passage) a worm to death, but it's not hard to spot maps with features like that, and even if you were playing on such a map, you should be able to avoid hiding in those susceptible spots.