OK, I believe that with any subject, as I said before, you can find a solution to make a stretto, but sometimes, if you have not thought it through, it is difficult or limited to the first notes, or you can only make two superimpositions.
Which is not bad either.
I have read @Fermata 's method and it is very good, although I put here something simpler and useful for any subject.
The idea is very simple: write, first of all, a subject that is canonical. Normally to the octave, but you can combine intervals.
That is to say: we write a canon.
Here I leave an example of how to build the canon to achieve three superimpositions (even if not at fixed times), to get the subject.