We all know that people at all stakes are capable of making adjustments, bad ones or good ones. This is true at all cash games, but especially so at Heads Up. Sometimes, comparing session stats to the overall stats for a particular player is not enough, as some heads up matches can last for thousands of hands and the adjustments could be made much more frequently to the point where the HUD is not representative of your opponent's game at all. For example, you have 5k total hands on your opponent where their 3bet % is 10. However, during a match he realizes that you are exploitable and starts 3betting much more than his 'standard,' throwing you off guard. You switch to session only stats and find out that he's 3betting 35% over the 500 hands you played. He realizes that you adjusted and starts 3betting at a lower frequency of 15%. At this point in time, there's not a lot you can do except make manual estimates.

So, how about a 'show stats from last x hands' option? You try to figure out how long ago they adjusted to you and your updated HUD shows you a more truthful display of your opponent's tendencies.