Intermediates on a single spreader mast?

[Brion Toss]

Hi again,
A small portion of the stay load is expressed laterally when the loads are highest (on the wind in a breeze), and the mast itself provides the needed lateral resistance. Your current intermediates are at such a steep angle that they provide very little lateral support, but impose a great deal of compression load on the spar. Runners will do about as well laterally, but will be far more effective fore-and-aft, given their wider angle.
As for placement, the more angle the better, but it is best if the end of the boom is aft of the runners, so you don't risk ripping the mains'l leach out in a jibe. Deck traffic is another concern, as you don't want the runners impeding that. House sides and other obstructions are also a layout consideration. And access for fasteners is another factor. All in all, this calls for careful design work.
Fair leads,
Brion Toss