This style of back is sometimes referred to here (in UK) as a fishtail. British military Mess dress invariably features a short jacket, whether stable or cavalry style, so high waisted trousers (some Mess uniforms have a version called coveralls) are essential. Worn with braces they ensure that the trousers hang perectly, but are also very comfortable to sit in. The higher waist also ensures that glimpses of shirt are not visible 'twixt waistcoat and trousers, for example when dancing. When I tried mine on for the first time I thought the waist slightly loose; the tailor told me he had made an allowance 'for the ravages of time and good dinners, sir'. His foresight has proved both accurate and useful.