AusBonsai

of course you could open up more available cambium, basically what you are doing is a ground layer, the roots will still come from the cambium edge, if you do a flat chop on the olive what you can do is cut the cambium/bark at a 45 degree angle, a chamfer i will virt later what i mean, and this will allow your roots to come out easier for one, and it will also show more cambium which will give you the oppurtunity for more roots, so instead of a flat cut that shows for example 5mm of cambium you can nearly double that by chamfering an angle around the base which will nearly double the amount of cambium, which in turn gives you more roots.

jamie

New roots start small, the same as new branches start with a small bud.
The bigger whole will not change the basic fact that the new roots will start small.
I believe you will have a ring of roots around your dowel not one larger root.
I used chopsticks one day when I was too lazy to go inside and get the toothpicks I just hacked my chopstick up with a pair of branch cutters. so I had odd sized pieces of wood, some chopstick size some dowel size.
Was a few years ago before I bothered to take photos. But the result was the same.

Roots won't come out larger, you'll just have more roots coming from all the way around each dowel.

You will still need to grow them out.

Please try this and prove me wrong.

Thanks guys, makes sense

regards

John