I must be a different type of Mercury in Cap because I am NOT all that technical or concerned with "what is".
I hated maths at school and barely tolerated science because i found them one dimensional and "flat". I was the type to look up into the sky and wonder about the universe and my place in it. So esoterical studies of the writings of old(Cap) appealed to me-hence astrology.
Anyone who has read my responses to posts will know that I am no "one line" man. Pretty verbose, i can go on for long on a question posed. This is not Cap in its purest form as Cap is usually stoic and brief.
I do tend to think of things in a very thorough manner(including spritual ideas) But am weary of superstition and dogmas that have no basis on my subjective experience.
My interest in global issues is HUGE (Mercury,Jupiter, Sun and Neptune in 9th).But I am also averse to watching news on "how bad it is" as am more concerned about the bigger picture of "why?"
Newspapers speak of contextual "facts". And Gem/Virgo Mercury or Mercury in 6th/3rd could be all about the details of "now".
Mercury square Mars-outspoken
Mercury parallel Jupiter-verbose
Mercury in 9th conjunct Mc may operate from both houses ime.
And as far as water mercury is concerned, I haven't experienced the open-minded thing you speak of in most. Even air sign mercury can be pretty bland and one dimensional in their views at times. Merely parroting others.
I don't know how many times my ideas have been thrown out as too "zany" by earth/water mercury alike. And yes earth mercury can be pretty "stick in mud" types. But not all.
I agree that house positions and mercury aspects count.