Unable to Specify Spawned Mob Sizes

I have set a command block to /summon minecraft:slime

{size:20}

. It worked in the previous update, but I wanted to summon a larger slime. However, when I put in another number it summoned the smallest size of a slime. I tried larger numbers, I tried smaller numbers. I even went back to size 20 and the result was the same: just a small slime.