Challenges of Playing on the High End - Tone
As blues harmonica players we prefer the tone of the lower keyed harmonicas and the lower six holes of the harmonica. When venturing above hole 6, the tone thins and we start to move off access of our cupped hands and away from our mic.
Players commonly use slaps as their default way to present the high notes for a more powerful sound. Using octaves (4 hole for blow and 5 hole for draw) is also a great approach for a bigger sound.
To help your amplified tone, move the thumb of your right hand with your cheek as you move right and allow the fingers to come along for the ride so that your cup extends as you move.
The study song "Blues for Paul deLay" http://www.bluesharmonica.com/lessons/tongue_blocking_5 is a great study to work on the techniques I've mentioned.