I've worked a lot with grips on heavy recoiling guns and agree with both Craig C and Boxhead.Thickness does distribute impact force but the most impact is at the top of the grip,in the web of the hand.I had a gunsmith friend in the early '70's that convinced me that grips should get smaller toward the bottom so that the two smaller fingers can wrap around better and this helps in control,during recoil.
So,when I build single action grips,they are beefier than factory at the top and slimmer at the bottom.This is a pair I just built for a Bisley.They are about .350 at the top and .410 at the bottom,then gracefully radiuse to the grip frame as Boxhead shows.
I've shown pictures before of the little,packing,.45 I put together with an aluminum,plow handle grip.The gun finished at 35 oz and there are no aluminum,Bisley grip frames available,so I needed the grips to help as much as possible to mitigate some decent bear loads.
I bought some 3/8" thick micarta,drew a centerline down each panel and maintained that 3/8" thickness,top to bottom.From that centerline,I gently radiused them,to the grip frame.I also reduced the flair at front and rear of the lower grip frame and what I got was a grip with plenty of meat at the top but slim enough at the bottom for the smaller fingers to get a good,solid wrap around.
I fired Corbon loads with 300 gr bullets,rated at 1300 fps and could easily tolerate them.There is a dramatic difference in felt recoil between these and factory plow handles.They don't have that nice visual flair when viewed from behind but don't look too much different from the side and they do work.
Oh,and they other thing I've noticed,the prettier the wood,the less pain I feel.