Had YOU been that DA40 on the day in question, you would have seen the other aircraft climbing crosswind (parallel with your track) in your 3 o clock position, range approx 1 mile/1.5 miles.
Have you seen the geographical photo's on previous pages ?
I have seen the geo pics and my thinking is that the RV wreckage site (and the area to its south east towards the children's play area and the A259 bridge) is a much better indicator as to where the collision took place than the other sites marked .. based upon:
a) the earlier observation in this thread that a prop can travel a significant distance when it detaches, and possibly other smaller pieces too.
b) Witness statements suggest the RV fell speedily from a low height (although we don't know what height yet do we - even 1100 feet might appear "low" to a muggle, as to "400 feet" - surely this isn't true but time till tell).
c) Witness statements suggest that the RV appeared to
turn away from the houses (on the east and south of the A259) and a bridge (which surely must be the A259 bridge and not the A27 bridge as quoted in the Mail article).
So if I was the DA40 joining crosswind (over the numbers and then tracking over the recreation park towards the A259 bridge) the other a/c would probably have been coming at me from below and from the left as it had just taken off from R20 and, the presumption here, made an agreed early left turn, in order to reach the point of collision.
But suppose, as you suggest, the RV had continued on a more 'normal' R20 departure, it still would have to have turned sharpish left and departed the published circuit track at some point, in order to approach me from my 3 o clock. But yes I would have stood a better chance of seeing it ... and it me. But I have several problems with this scenario so it seems less likely to me - based on what we know.