Prior form over two miles proved the ultimate factor for Knight as she opted for the Champion Chase over the Ryanair Chase, which is contested over an extra five furlongs.
The decision has ensured that Somersby is now the third favourite in the Champion Chase betting behind Master Minded and last year’s winner Big Zeb, who are 2/1 and 7/2 in the Cheltenham betting market respectively.
Knight highlighted that the Cheltenham Festival was not the right place to experiment with horses in terms of running over an untried distance.
She added: “We’d look like right prunes if he ran in the Ryanair and the trip didn’t suit him – it would be madness to try him at a distance he’s never run at in that type of race.
“He has never run a bad race at two miles, and we can always go further with him next year.”
Entry into the Champion Chase also presents Somersby with the opportunity to gain revenge on Master Minded.
The pair clashed at Ascot last month over 2m1f in the Victor Chandler Chase, with Master Minded hanging on in the closing strides to secure victory by a short head.
This result was one of the reasons why Somersby was being considered for the Ryanair Chase, as he showed the reserves of his stamina when running on gallantly in the closing stages.
Somersby has also previously shown form at the Cheltenham Festival over two miles when finishing second in the Arkle Chase last year behind Sizing Europe.
A £25 stake on Sizing Europe winning the Queen Mother Champion Chase would return £400. New customers can sign up here for a free £25 bet.