How would you rank the importance of the letter-place in a type?

For example, I think the 4th letter is the most important, followed by the 1st, then by the 2nd, then by the 3rd.

And a letter would be most important if it would impose the greatest difficulty on relations should it be different, while the other three were the same.

So, by my example, it would hold that an INTP would have a harder time getting on with an INTJ, than an ENTP. To extend that, a list of types sharing 3 letters, from best to worst relation with an INTP, would be:

INFP
ISTP
ENTP
INTJ

And for an INTJ, it would be:

INFJ
ISTJ
ENTJ
INTP

So the INFJ would be the best option, of the four, for the INTJ to interact with.

I'm trying to see what is the most important letter-place; I'm just using the types as an example.

What do you think?