Use /usr/local/portage/, not /usr/portage/local/.
The directory /usr/portage/local/ was the old way of doing it, but was changed as the default in layman last year (see e.g. the thread layman -S does not detect linux-sabayon-2.6.26 [Solved]
In /etc/make.conf you should have the line: source /usr/local/portage/layman/make.conf
In layman.cfg you should have /usr/local/portage/layman/ defined as the overlay directory.
and PORTDIR_OVERLAY should use /usr/local/portage/
so it should be:
or, better still, right at the end, as:
(To go into detail, it actually does not matter which directory is specified so long as it is consistently specified in ALL config files. However, as the default sources directory in the as-installed layman package was redefined last year as being /usr/local/portage/ then it makes sense to stick with that.)