Ukdame,
The hole on the Supreme Slider is only wide enough for the needle itself (that small space where the needle reaches down into the bobbin compartment (maybe 1cm x 1cm) It should cover up most of your needle plate & everything else on the base of your machine.
I will add that you also need to consider friction on the surrounding surfaces supporting your quilt -- especially if your machine is not sunken or surrounded by an extension table. I made my own DIY extension table with Whitman's Chocolate Boxes (it was a sacrifice to have to eat all those chocolates -- but it was worth it to further my contributions to the world of quilting
. I just put them solid side up & taped them with masking tape to the bed of my machine (under the Supreme Slider).
I also found that putting my machine on a slight tilt (many people use doorstops; I just grab a roll or two of masking tape and tuck them under the back edges of my machine) helps the quilt move more smoothly. Probably part of that is that I can actually see better.