Wonder wads will work, but you want to use the next gauge size larger in that 20( 19, or 18, if they have them) to make sure of the seal behind a PRB to get consistent velocity and lower SDV.
Using a Vegetable Fiber Wad( See TOTW) will also provide a good seal, and contribute to complete burning of your powder, whether shooting Swiss or Goex.
The OP wads reduce the SDV for both powders, and make for smaller groups. You have to measure the bores of your guns with a caliper to know the EXACT dimention of the bore. .20 ga. barrels tend to vary from .610-.627" in diameter. Nominally, the bore should be .615". Wads are usually .620-625" in diameter.
I had to order 19 gauge OP wads to get a good seal in my 20 ga. fowler. If you are not using a chronograph, you may never find that exact same load that shot so well for you, again. But, you can work up loads with either powder to get the best accuracy possible.
Try greasing the bore in front of the PRB by running a greased cleaning patch down the barrel, either on the jag when you seat the PRB, or afterwards, using an additional stroke with the ramrod. We found that velocity is increased by about 20 fps, on average, and the SDV in velocity was cut in half!
Do not switch patch lubes, or how you put the lube on the patches, or change patch material. Each can destroy your group size. Check the thickness with your calipers on any new batch of patches you buy, or use, to make sure they are the same thickness as what you have been using. DO NOT TRUST the labels on packages for giving you the correct size.