If you "scan the magnetism" for the whole width of the tape -- which such a generic reader for magnetic tapes would have to do anyway -- you can parse out such things after the fact.

    adg.
    .beh
    ..cf

Even if your input is "a..db.gec.hf", that should be able to postprocess out later, for any possible angle, given enough resolution.

It's a lot like decoding music from vinyl grooves based on a 2D image scan of the vinyl.