The location of <aiin> and <ain> groups

[Common_Man]

/m/ sound i believe is articulated in the lips, so it is "bilabial" nasal sound, and you should compare the bialbial part with the velar part of /k/ and /g/.

Also /n/ sound is articulated at the "alveolar" region, so that being resonated through the nasal chamber doesnt mean it should be taken as just a "nasal" sound, but rather as a "alveolar" nasal sound.

So it seems that the term "nasal-valar" collapse doesn't make sense, and what you should've been going for was a "labio-alveolar-velar" collapse, which makes even lesser sense..

There are voiced nasal plosive sound variant for every place of articulation (I know this as I can speak 2 indian languages, in our alphabet we have series of consonats based on places of articulation starting from velar, through palatal, pre alveolar, alveolar/dental, and labial, I maybe wrong here though, and all the series have nasal variants). 

But I did like the idea of alveo palatal collapse pit forward by Derek at the Stephen Bax forum..