Also (in my own weakly-asserted opinion) a third pinnace (or ship's boat) would mean that the three small craft would have a combined total of 600G-tons of thrust. [EDIT TO ADD: (5G x 40Td = 200GxTd per pinnace, 6G x 30Td = 180GxTd, round up to 33.3Td and it could be providing 200GxTd as well) ] This could have accelerated the ship at 1G, if the acceleration constraint otherwise was that the normal docking points were off-center
To clarify: when looked at from the aft end, the pinnaces on the pylons are "way up there", and another in the nose dock would be "way down there". If all three were present, it'd be almost balanced. If all three were pushing, the ship would go in a straight line.
On the other hand, just two mounted on the pylons pushing would either cause forward somersaults, or they'd both have to be pointed nose-down -- and it'd look like the ship was "popping a wheelie"; alternately, a single one in the nose dock would need to be docked sharply nose-up (tail hanging down) to point through the likely center of mass. The deck plans and illustrations don't suggest that's possible though.
The question then is whether the stated 0.1G limit is due to:
a. Inefficiency of small craft drives pushing a starship hull as tugboats (that is, something about the drives themselves)
b. Off-center locations of small craft docks; small-craft drives can't thrust-vector very well (that is, it's about their position)
c. The pylons aren't strong enough to support 200G-Td of thrust each on the mounting points
d. The collector sail is fragile and will be damaged if subjected to more than 0.1G when folded (let alone when open)
EDIT TO ADD: This is with respect to the Double Adventure 1 deck plans, not the MgT High Guard version. The latter plans did not include a nose dock in the cargo hold deck.