It’s important to remember that the shape plays a roll in the fit, and not every brand’s sizing runs the exact same, which are both reasons it’s helpful to try things on in person or work with a fitter virtually.
I can personally vouch for Nordstrom and Bravissimo’s online bra fittings. I found both experiences to be very helpful in finding a properly fitting bra and the fitters made me feel comfortable during my appointments.
For your virtual fitting, all you need is to be wearing a bra! It helps to have good lighting and a camera set up that allows you to be hands-free. You’ll want space to move around to show the back, sides and front of the bra.
If your bra gaps, the first thing you should do is a good swoop and scoop of tissue to the front of the bra. If it’s still gapping, it could mean that you need to go down in your cup size or that you need to try a different style of bra.