Are you using IPS panels? They seem to work much better in portrait than TN panels do. (I have 3x 24" IPS panels in a portrait-landscape-portrait configuration

Are you using IPS panels? They seem to work much better in portrait than TN panels do. (I have 3x 24" IPS panels in a portrait-landscape-portrait configuration at work, 2x 24" TN panels in landscape-landscape at home.)