I believe it is the position of the pelvis that will determine which ‘direction’ you are stretching. SD while standing should be the same as sitting unless you are sat leaning forward or backwards. The best angle for ligs is BTC, pull through your legs and between the cheeks to get this effect.
The reverse kegel portion of the blaster will give you benefits with downward stretching, so DLD blasters do not need to be modified with this angle. If you like, you could ditch the normal kegel, but some people find it useful to do it in order to feel the difference between doing an RK or not. When I made my gains I was not doing normal kegels, just RK for 5 secs, relax 5 secs, repeat.