Going from a three to four ton unit was a mistake. One that's easy to make because it's counter-intuitive. And because bigger units are more expensive there's a sales incentive to sell bigger units too. To be effective at cooling
people an air conditioner needs to remove latent heat in the form of water vapor. Lowering the air temperature isn't enough.
Oversized units short-cycle, lowering the air temperature significantly faster than they remove latent heat by condensing water vapor. The controlling thermostat turns the unit off quickly because the big unit quickly reduces the air temperature. The latent heat in the water vapor remains in the air. People still feel hot.
Basically, a residential air conditioner should be running most of the time if it's properly sized. Oversized units will come on, run for a few minutes, shut down for a few minutes, run for a few minutes, etc.
Double pane windows and blown insulation will magnify the effect because the air conditioner will reduce the air temperature more quickly and efficiently and leave more latent heat in the air.
Note that latent heat in the air from water vapor increases with temperature. That's why we talk in terms of relative humidity. So oversizing is less of an issue for heating season and double pane windows and extra insulation help.