Jeff_e_d
Can't give you a definite answer w/o the doiwnrigger you're going to use and actually working with them.
I'd get the base, set it on the available area, then with the downrigger I was going to use, move them around to figure out the most efficient location for operating the downrigger, keeping in mind to allow for operation of the cleat with the dock lines, and keeping the two from interferring with each other.
Too complicated for a point-blank answer w/o the exact spatial relationships involved.
Joe.