Hey Bob, don't feel badly if you don't get it. It is confusing. In your example, if the Bb horn plays an Eb scale, it will be sound as a Db concert scale, not F. Since the horn is pitched one full step below concert pitch, the notes it plays when reading concert pitches will be one full step below concert pitch. If you want it to sound a concert pitch, you have write a note one full step above concert pitch to compensate. To hear a concert Eb scale from a trumpet, you write an F scale.

The reason I chose to write about the fingering issue, and not the tube length and fundamentals etc., was that there are a few exceptions. The trombones for the most part read bass clef and are taught that the open fundamental is indeed C, rather than Bb, even though the horn is pitched an octave below the Bb trumpet. So it can be done the way you say. Similar thing for baritones. Some learn bass clef and pitch it in C because they started out as trombone players. Some (like me) learn treble clef and Bb, because they started out on trumpet. When I write a part for a baritone horn, I first ask them which clef they want, and that tells me how they interpret the horn. Usually.

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