I have a fuzzy lop too! I try to groom her at twice a week (more if she’s going through a molt) to stop mats from developing but regardless she still gets them on her rear end/tail area too!
I have found that having another person help holding the bun while you groom the sensitive areas is helpful. I get my mom or my boyfriend to hold her whichever way it makes it easier to get at the mat, either on her back or just holding her still in her normal position. If the mat is really dense and can’t be brushed out I take a very small pair of scissors and clip it out.
If the mat is still really close to her skin I wont clip the full mat out but clip half of it and wait for her hair to grow a little more before I try to get the rest. I usually measure with my thumb. If there is a thumb-width between her and the end of the mat then I will clip it all otherwise to avoid clipping her skin by accident I just take out what I can and wait until it has grown out farther.
You have to be careful and my Smudge doesn’t always enjoy the little clicking sound of the scissors, I rarely try to do it by myself I like to have one hand in control of the scissors and one had feeling where her skin is the whole time and guiding the scissors. Another thing you can do is place your fingers like “scissors” over the top and bottom of where the mat starts between it and her skin (hope that makes sense!) and cut against your own fingers that way if by chance you did slip you would hit your own fingers and not her… chances are since you can feel the scissors against your skin you wont slip up anyways.
Hope this helped! If I didn’t make sense let me know lol.
edited to add: another tip – if you can cover the buns eyes either with the hand of the person holding her or even wrap her up in a towel around her body with her back end out for grooming and use the edge to cover her eyes, it can help calm them because they can’t see what’s going on. You could also try trancing it she’s really skittish about letting you touch her. Have the other person hold her on her back and rub/pet her nose and head. Some buns will trance easily, others don’t and some will be come out of it if they’re touched. There’s alot of different opinions about what trancing actually does to a bun but in a pinch it can work 