User not detected when calling shell in remote dired

[reza <reza@housseini.me>]

Hi all

When I open a remote folder with dired C-x d /ssh:myuser@myremote and 
call M-x shell there, emacs displays in the minibuffer

Remote shell path: /ssh:nil@myremote:/bin/sh

and I have to manually override my user. How can I instruct emacs to 
pick the correct user or even pick up the user from my ~/.ssh/config file?

And is there also a possibility to change the default remote shell?

Thanks for any help!

Best,
Reza