Sheri, mucho thanks for the css tip to force a fixed vertical banner image size in Bushwick.
Passing along this change in custom-header.php to make this happen:
@line 62 in custom-header.php (in the <?php if ... clause) I changed background-image: cover; to background-image: auto;
@line 100 also in custom-header.php (in function bushwick_admin_header_style(), I changed background-image: cover to auto.
Browser compatibility issues however:
Works in Chrome and Firefox (don't have a Mac browser to test at this location, will test on my one of the Mac users in my org) but breaks in IE 10 and 11? Need a compatibility fix I guess to cover those people still stuck on IE!