The Desiderative san gets the augment iṭ after the root kṝ - tudādigaṇaḥ (6th Conjugation) and the four roots that follow it.,
Thus चिकरिषति, जिगरिषति, दिदरिषते, दिधरिषते, पिप्रच्छिषति 1.2.8; (VI. I. 16). But सिसृक्षति not included in the five. The roots कॄ and गॄ would have optionally got इट् in the desiderative by 7.2.41, which would have been optionally lengthened by 7.2.38. But the इट् here being specifically ordained, does not get lengthened by 7.2.38.,