I wouldn't make that conduit much longer than the original design. The bigger the circle you make the more work it is and the more movement and the more you'll be busting knuckles against stuff. (Tight spots, trees with two trunks, spots close to limbs etc.) Leverage hasn't been an issue at all for me with the original design.
I have had issues with harder wooded trees were a little more torque would have helped and the thinner material would have bent on the drill if I had forced it.
I would say it isn't more work just different (someone who likes physics can do the math), as in yes your arm will rotate around in a circumference 6in longer each turn (at 6in radius vs 7in) but the number of rotations is the same, and it'll be less effort over a greater distance as opposed to more effort over a shorter distance.
If your working in a tight spot the drill can open at an angle greater than 90 effectively decreasing your working area, but yeah don't go too much bigger than the original still or it will become unwieldy. But I feel like the original was made to be as small and light as possible, just barely long enough to have a section with uncut pipe for rigidity and also the same length as the bolts (which is nice) and long enough to turn but not necessary engineered to maximum performance. But here is my reasoning:
-thicker/larger pipe (Pros - stronger, longer lasting, less chance to ruin a hunt from breaking, dip-able for silencing. Cons - slight weight increase)
-slightly longer body (Pros - easier to drill Cons - slight weight increase, slightly larger rotations, slightly larger packing size)
So for me the weight isn't a huge issue, first because it is still super pack-able and light, a solid product I can depend on is much more important.
If anyone decides that ~7in is too long for optimum use you can simply cut the handle end some more and re-drill the handle hole without remaking the whole thing.