Mold venting for lost foam metal casting

I've been casting small aluminum statues using the "lost Foam " technique. My success rate has been about 60%t070%because of the aluminum freezing in the long narrow parts of the mold. The statues are human figures so the outstretched arms and legs sometimes are not complete. Am now considering heating the mold to reduce this problem. Any suggestions will be appreciated

one thing will help is adding a vent from the pieces that are not forming, thus allowing the casting material to more easily flow into the small areas. From the end of the outstretched arms is a good place. you then clip off the extra material and polish down the area it was once attached to.