I made all mine, when I made them, with two holes the size of a quart jar lid so I can feed through the inner cover. Then covered the bottom of the hole with #8 hardware cloth so I can fill jars without facing bees. that way I don't even have to suit up or light a smoker when feeding. The reason for two is it's more likely I can get the feeder over the cluster when the weather is marginal.
The reason for the shape in the standard ones is to fit a Porter bee escape, which are not very common these days I don't think.