Reduction SDK question?

Accelerated Computing CUDA CUDA Programming and Performance
1

In the reduction SDK example they have 7 different kernels(kernel 0 - kernel 6) which have different optimizations. I however noticed the following in the reduction.cu file:

// execute the initial kernel

	reduce<T>(n, numThreads, numBlocks, whichKernel, d_idata, d_odata);

	

	// sum partial block sums on GPU

	int s = numBlocks;

	int kernel = (whichKernel == 6) ? 5 : whichKernel;

		...

If you specify the use of kernel 6 it does the initial part of the reduction on kernel 6, but then for the rest of the reduction it uses kernel 5. Why is this? Thanks