Lightbox help - frameless picture size

I Need Help
1

can anyone help with how I can increase size of images in the framless lightbox option?
ie. somewhere between full screen and frameless default size -

for some reason the image is still scaled down when clicked from the gallery (have tried alternative image option also but still scaled down)

thanks in advance!

2

I normally use either 1600px wide for most of my galleries.

casey