In order to remedy this, I created a "hockey puck" of scrap aluminium to sit between the DEC assembly and the adapter plate. The puck measures 3.5" x 0.75" with two through holes spaced 3" on center.
The puck is the bright silver colored part in the images below. You can see that with this puck, the adapter plate just clears the motor housing in this position. In fact, there is now no orientation in which the adapter plate collides with the motor housing.
|Near North Horizon - Mount on East Side|
|Near North Equator - Mount on East Side|