on my current chair depth is 18ir the backs of my legs hit the cushion so my dme shortened the upholstry and notched the corners of my jay 2 cushion by 1 and a half inches

im in the works of getting a new chair i measured from my butt to the bend in my knee and have about 19and a half inches should i go with a 16 or 17 inch chair depth my dme says 18 and cut the cush again but im not doin that again and the 18 inch demo im uing is definitly rubbin the backs of my legs

any advice would be appreciated