I agree with Paul.
Nothing prevents in the spetifications to shape the top of the T sections to runner body allowed measurements.
Also I feel it was intended to otherwise it would leave a sharp edge on the side of the runner if it wasnt. That could couse severe injuries by accidents.
On the other hand spetifications mentions the T section dimensions. The front of the runner if tapered, wont fit the allowed T section dimensions.
So, in a way David is right.
It seems a glitch again in the specs.