i hate to be a naysayer, but i sure wouldnt count on just a silicone to keep more tiles from cracking. that is too much flexing.
i was paranoid about cracking when i put granite down.
on a recommendation from a wanderlodge fellow who does lots of floors in coaches, i used SAM3 from NAC
http://www.nacproducts.com/Sam3.htm
as an anti cracking membrane and then used mapei ultraflex2 thinset for the granite.
then i called newell and asked what they used for grout and they said silicone. so i got the silicone from the tile company that is matching to the grout color we wanted and ALL of my grout lines are pure silicone. it makes a mess, but is totally flexible.
from two years of useage, no cracks.
tom