What are the phonotactic rules of 促音 in lexical items?


In comparison to 連濁, finding rules on 促音 seems much harder. If possible, I
would like to figure out what the rules are, that is, in which positions 促音
_can_ occur, and in which positions 促音 is _likely_ to occur. (Limited to
Kanji-only words, that is ignoring phenomena such as っ for emphasis or elision
in speech, e.g. っす)

For most words, these rules seem to hold:

  * 促音 not in word-initial position
  * 促音 only in the last mora of a morpheme
  * 促音 only in two-or-more mora morphemes
  * 促音 only rarely before some suffix morphemes (者, 的, the like)
  * 促音 only in /u/ or /i/ based mora

I have also observed:

  * The rarer the word, the less likely it has 促音

It might be the case that:

  * More 促音 in 音読み words

The general pattern is: C(u/i)CV -> っCV Seemingly, most consonants can only
reduce in front of the same consonant (so がっこう), but つ and ち seem to be able
to reduce in front of the same consonant.  
つ and く seem to be the most likely to reduce, but perhaps only because they
are the most common.

Incidentally, these rules seem pretty similar to 連濁.

Are there other tendencies that have been observed, e.g. via corpus analysis?
Are there other rules?

