Ruddy - Wood at a given thickness can only bend so far before it takes set. Fact! You make that piece of wood thicker and it can only bend to a lesser degree before taking set. Make your piece of wood thinner and it can bend further....again these are simple plain facts!
Now look at an elb......notice the large thickness taper. Apply those facts to a tapering piece of wood.
The tiller shape for an elb should have a little bend through the handle (depending on what you want the bow for, target only a little less bend is ok) and as the wood gets progressively thinner towards the tips the bend should be increasing proportionately.
Marc - the bow should take more set in the outer limbs? Why would you want set in the inner limbs? Any set there would have a negative effect on string tension and therefore performance. All this talk about getting this part or that part of the bow to do more work is a misnomer the whole bow should be working evenly. EVERY part should be strained to the same level, afterall wood doesn't know where it is on a bow it only knows the strain it is feeling and will respond accordingly eg. set or not. I don't hold with what you say about the part where there is most wood should be doing the most work. If you did a strain analysis of this bow I bet you would see that the inner limbs/handle area is doing plenty of work! My guess would be about the same strain as the outerlimbs. That handle area cannot bend much because if is a thick piece of wood BUT you can bet your bottom dollar that it is strained it certainly isn't sat there doing not much.
It's not a compettion of who's made the most bows you know! I only said that because I see a load of comments from people who clearly haven't made what they profess to know about and I was just quantifying my statement. I won't comment on things i'm not certain about.....I'm sure you have made many bows and are very good at it!