According to the both releases of the AJS 37 manual, the approach altitude of BK-90s can be selected using TAKT Input 91XXX0, where XXX is the altitude in meters. The following video shows that regardless of what that setting is, the dispensers approach the target at the same height as they do by default, 400 feet. (However, the area of effect pattern is programmable with 92X000.)
For comparison, here is a video of the same mission, with no TAKT inputs. Interestingly, the approach altitude of the dispensers seems to be 400 ft, despite the manual saying it is 60m (about 200 ft).