Perhaps the best companionway location, from a bluewater sailing point of view, would be a hatch near each crossbeam, with the ability to climb down directly to the main galley level or further, to the "Dressing Room/Cabin" landing and the head below.
It almost goes without saying, but to be clear from the start, a raised entry like this is a significant obstacle to air and water flow, so not ideal at all for bluewater cruising!
As a proa gets larger, it makes sense to allocate more of the bridge deck area for internal use (accommodations). However, this increases the distance to be crossed before stepping down into the main hull, since ~70' isn't big enough for enclosed full standing headroom (as far as I'm concerned).
Possible solutions include two entrances instead of one (intrusive on limited interior space but makes sense for hatches near beams) or moving the mast to windward of the cockpit and out of the way of a single, central entrance.
It is inevitable, however, with or without supporting a mast, that some kind of central access like this will be used - passing between two tables for three that are easily joined as a table for eight. Need a lower, thinner, wider (windward/leeward), smoother curved beam to support the mast...?