Stockhausen mentioned in the second hour of his composition course (Monday, July 10, 2006) that his composing in KLANG was a return to moment form after his period of formula composition, which had been preceded by moment composition from the early 1960s on. In the Q & A session I asked Stockhausen:
"Is HIMMELFAHRT not a mixture between formula composition and moment form (moment composition)? The reason for this question is the following: in formula composition the formula is used as melody, but also stretched over larger parts of the work, and even over the entire duration. In HIMMELFAHRT, there is on the large scale, stretching over the entire duration, a so-called tempo melody 1) which, as you explained, is derived from the pitch melody on the small scale 2). In that sense, the pitch melody indirectly informs the large scale as well, just as in formula composition."
Stockhausen’s answer (reproduction based on both my own memory and on discussions with others about what they perceived):
"In one sense HIMMELFAHRT is a mixture of moment form and large-scale form, because of the tempo melody over the entire duration, but there is an essential difference from formula composition. The formula is not just the pitches but also the durations. In HIMMELFAHRT, on the other hand, durations and pitches are independently composed, which allows for more freedom. In some early compositions there was also more determination of the overall form by the pitch structure than here."
(One day later, Stockhausen confirms the issue of independent pitches and durations.)
1) see CD cover, which can also be viewed at: http://www.stockhausen.org/cover_cd_83.jpg, red: tempi for the right hand, blue: tempi for the left hand)
2) see composition booklet, p. 20 f., for details