size picture top of the post

Hi,
about the top picture display automaticaly on top of the post :
I don’t understand what size is display because :

http://test.sophronisator.fr/lancer-lapplication-sophrologie-accord-sophro/
this display image withe computer is truncate on the height, and I test with different size of picture larger heighter, impossible to have the complete image.(not cut)
how can I display not cut
but :
http://test.sophronisator.fr/initiation/

the display image (it’s me ;) ) is too big and there are not issue with the height ? how can i reduce this size ?

other pages seems to be OK (the picture is 16/9) ?

Can you explain me the process to have a correct picture display ?

Best Regards
cm

ps :
I tryed this in style.css find in your doc :
#top.single-post .big-preview {
max-width: 600px !important;
margin: 0 auto;
}

There are big cache issue but finaly I have always the issue.

I just remove this css.