HI,
I asked this question of a couple boa breeders in the States and they both replied , they prefer using smaller males to a larger female this results in more active breeding by the male less problems for the female and larger clutches if kept at the right temps. Most females have lower amounts of slugs if kepta little warmer during the pregnancy.
I ve never bred boas to date ,, just interested in a positive outcome.
here's a pic of the parents of one of my boa's that are owned by a MR C. English in the states,, ps the males the smaller one.
There are nice looking boa's in the states I just don't know how to get them in Canada thru customs.

.
Doug
here's the owner of the parents he has some awsome boa's I own one BCI and two hog island boa's that are the product of his breeding projects.
http://www.redtailboas.com/current/index.html