yup, two different types of benefit from the WMI.
Injecting early gives the biggest cooling benefit as the mixture has time to atomise and cool the charge.
Injecting late into the inlet manifold works better with higher concentrations of meth as you're mainly using the octane benefit of the meth.
Both have similar results in that more timing can be added. On a road or track car I'd go for single port injection just post IC. On a car used for drag racing I'd go with direct into each inlet runner.
I plumbed mine in like this:

