This is 910mhz, right? The only thing I can think of is that Alex's measurements for the cloverleaf antenna on the long piece of wire was 26.5" and the SPW shows 26.0" which might explain why your SPW has a bigger overlap. I would also check your measurements on the legs; they should be 84mm each.
I'm just guessing here, but checking those measurements is where I'd start.
Then again, if the antenna works well, maybe you can just go with it!