Mine varies with signal strength. Bars/dots are a poor way to determine signal strength. If you are at a wifi site for extended time like home and you want to turn on wifi calling just select airplane mode and turn on wifi. My att LTE signal is week at home. Att wifi is much stronger, so I turn on airplane and then wifi. Phone defaults to wifi calling with stronger signal through my home wifi. Battery lasts much longer as well.
Weird part is how fast wifi calling is. Usually connected before a ring. Also seems to me, much clearer sound on wifi calling.
Another way is to turn off cellular. My signal is one dot with cellular, and five dots when I turn off cellular and let it do only wifi calling. Odd part is it doesn't say wifi calling, but is as cellular is off and calls still come through, and much better than with cellular on.