pin/pen merger, a question...

[Douglas Bigham]

Here's a question I've recently ran into and I can't either find or invent an answer for it.

What are the rules for the pin/pen vowel merger?

I've got the merger (and when I try not to it comes out pin/pan) but I still have the low-mid "E" as contrasting with "I".

ex. with the merger:

ink pin vs stick pin
alphabit (alphabet)
nixt (next)

However, I can place a bEt on the horse with the prettiest bIt.  And, I can nick (I) my neck (E) while shaveing.

Furthermore, If I attempt to say alphabet (E) it doesn't make any sense (like there should be a beta bet, gamma bet, etc).

Just wondering what the rules (if any) there are for merging.

-dsb
Douglas S. Bigham
Southern Illinois University - Carbondale