One puzzle of Meyer's rapier treatise is that he frequently refers to a position called "Straight Parrying [gerade Versatzung]", especially in part two of the treatise, despite the fact that it is not listed as a guard in Chapter 3. It is defined in the Dusack treatise as follows:
Stand with your right foot forward and hold your dusack in front of you with your arm extended, so that your long edge stands toward the opponent and the tip of your weapon is forward...
A picture is referenced (F), which does indeed seem to match the description, adding that the guard is also held high (chin height). Similar images occur in other plates. Unfortunately, Meyer's guards aren't necessarily the same between weapons forms. One example is Eisenport [Irongate], which is point up for the Rapier, but point down in the Longsword. Furthermore, there is a picture of Straight Parrying in the Rapier section (again, plate F). It does match the description above, however the figure has a more extended weapon and is himself further forward (almost like the end of a lunge), and the weapon is held somewhat lower (solar plexis).
Apart from the very forward, extended stance, the position in the picture is similar to Eisenport:
Stand with your right foot forwards as always, hold your weapon with your arm extended down and forward before your right knee, so the point extends forward up against the opponent's face....
And here's a picture (C). The uses that Eisenport and Straight parrying are put to are similar, so they do seem to be similar positions. In a number of places, Meyer says things like "...if an opponent stands before you in Eisenport or Straight Parrying..." so possibly they're even synonyms. This might be misleading, however, as sometimes Meyer uses similar constructions to show variety and/or versatility, e.g. in the Neck cut: "...hold your weapon on the right in the Low Guard or Eisenport...".
From these considerations I formed the following hypothesis: Eisenport and Straight Parrying are similar, and put to similar uses. Straight Parrying differs in that it is held higher and with the point higher. The picture in the Rapier treatise plate F is misleading.
Then, I made one discovery and realised one other simple fact. The simple fact is that in part 2 of the Rapier treatise, Meyer discusses devices and tactics from Straight Parrying, High Guard (left and right), Low Guard (left and right) and Pflug. That is, everything except Eisenport! In fact, the term "Eisenport", frequently appearing in part 1, almost disappears in part 2. The "discovery" (of a purely personal sort, I'm sure) was another picture purporting to show Straight Parrying. It's the two guys at the back in plate C, (Eisenport is depicted at front). They appear to be in Eisenport!
Conclusion: Eisenport and Straight Parrying are synonyms, and the guy in the middle of plate F is still misleading.
p.s. I'm working (as usual) from the Forgeng translation.