Gittin, and the Separation between Bamidbar and Devarim

The first Tosfos in Gittin brings from the Geonim Rav Hai and Rav Saadiah that a Get needs to be written in twelve lines. The Torah refers to a Get as a Sefer Krisus, a Book of Severance, or a Book of Separation. We interpret the word "Sefer" to be a reference to the Sefer Torah, and the word Krisus to refer to the the four lines which separate each book of the Torah from its neighbor. Since between the first four books of the Torah there are a total of three separations, and the three separations yields a total of twelve lines of separation, a Get, which is called the Book of Separation, should be written in twelve lines.

In other words, the Get creates division and separation. The lines that separate in a Sefer Torah are, in a sense, made manifest in the Get, and they generate separation between the man and the woman.

Of course, the question that immediately presents itself is that there are four separations between the five books, so the Get should be written in sixteen lines, not twelve. Why only focus on the three separations between the first four books?

Tosfos answers that we don't count the lines of separation between Bamidbar and Devarim, because Devarim is just a reiteration of what has been said before. The question, however, seems to be far better than the answer.

I recently saw a suggestion that we don't count all four lines of separation between the books. All parshios are separated, and parshios pesuchos have a blank line separating them from the following parsha. If so, it was said, we don't count all four lines between chumashim, we only count the extra ones, namely, three of the four. Four separations, three lines each, total of twelve. Voila.

This answer assumes that the standard parsha pesucha separation line is separate from the Sefer separation lines. This is not necessarily true. Let's imagine that the halacha leMoshe MiSinai required there be four lines between chumashim, and there be one line between parshios. One of the four between chumashim could also serve as the one between parshios. In other words, the answer assumes that the halacha was that we needed three between chumashim, and we added another because we need one between parshios. This is not necessarily so. It could be that the halacha requires four, but one of the four does double duty, since in fact the separation exists.