The seventeen entries with definition-only clues are to be treated according to a symmetrically disposed theme which has to be highlighted. Other clues are normal; all enumerations are of entry lengths.

Across

1 Bothers about losing, initially, eight pounds (6)
7 Help senior NCO when cutting hair (6, two words)
11 Wallop maker (10, hyphened)
13 A salt (5)
14 One fetching (5)
15 It, beer, runs over slacks (7)
17 Recess (7)
18 One races by whichever French province (6)
19 The beginning (4)
22 E.g.