I'm not trying to argue with you, but I have known Brits and Aussies to do that very thing--write
AH for "a" as in "cat" and AR for "a" as in "father." My only point (as this relates to the original post, on the pronunciation of
Kari) is that it's very difficult to use standard alphabet symbols, or even words that supposedly rhyme, to express vowel sounds in any way that will be self-evident to speakers of various English dialects. To use your own examples, in my dialect the "a" of "father" is by no means the "a" of "past," nor is it the same as in "cart," so using
AH to represent all three of those sounds would be essentially meaningless.