laying side Leg raises for dynamic flexibility?

[grr]

Hello everybody. I just got Thomas Kurz book and im really enjoying it. Im having problems though with the side leg raises.I understand It will come with time, and In the book he suggest using a chair if needed to get more height but I find if I lay on my side and do the standard leg raises I can get the most height.Will I get the same results as if Im standing and increased flexibillity or is more a strength issue why I cant raise my leg higher standing but can lower?