Change portfolio hero image on hover

Website url: https://www.ascentbuildingco.com/template-projects

In the project template I want the hero image of each project (in the grid) to change on hover to a specific interior shot.

For example with the Windfall project, on hover it should change from 

to
 

https://images.squarespace-cdn.com/content/v1/5479fbb6e4b09ed1ced6da1d/3b6169ed-fc81-4b25-aeb7-3ab1c372592e/60_Ascent_2016.jpg

I've added the following code and it pulls in the right image but it is tiling it. I know it has to do with the "format=100w" at the end of the code but i'm not sure which number to change it to so it's full width

/* Change image on portfolio item hover */
a.grid-item[href*=windfall]:hover img {
    visibility: hidden;
}
.grid-image-inner-wrapper:after {
    visibility: hidden;
}
a.grid-item[href*=windfall]:hover .grid-image-inner-wrapper {
    background-image: url(https://images.squarespace-cdn.com/content/v1/5479fbb6e4b09ed1ced6da1d/3b6169ed-fc81-4b25-aeb7-3ab1c372592e/60_Ascent+2016+Print.jpg?format=100w) !important;
}