The idea is to keep the humidity high around the cuttings BUT you also need circulation to prevent fungus from growing on the soil or cuttinge. The gaps will not hurt & remove covering several times a day for an hour or so

When doing only a few cuttings, I put them in 4 inch pots, use a stick of some sort to hold the plastic off the plant, and stand each one down in a cheapie gallon bag. You can then tie the bag shut around the stick or leave a bit of an opening. I have a single shop light set up for these odd propagation jobs that come up along the way.

Another little trick that helps is to keep a quart (or smaller) spray bottle filled with a mix of 1/4 t. baking soda and a few drops of gentle dish soap. This spray will kill molds and mildews if you see it forming. You can add 1/4 t. of something like Miracle Grow to the mix and spray the cutting...foliar feeds as well as mildew/mold control. I use it to spray the inside of the bag before inserting the cutting to get the humidity up and prevent disease.