Can you change runners to go back to the maw as soon as they get a artifact? Something that happens surprisingly often is you have a runner get right beside the maw hit by a rock and instead of picking up all they had it gets spread out between a few runners. Instead of bringing it like 3 steps to the maw they bring the artifact all the way back to the gold pile and have a chance of having the process repeat itself.
Actually a even better change might be to have runners that get hit by something remember what they were carry it and claim it ( or the nearest unstuned runner) so other runners ignore it avoiding the situation of bringing gold back the the gold pile ( except in the case of the maw getting clogged but you said you are fixing that anyway with a vacuum upgrade or something, also a exception of if they get full of ore before they reach all of what they were carrying)
Another way to do it is if a runner has 1/2 carrying capacity and are closer to the maw then the next ore then go back to the maw early