I believe it is a true angled channel, from what I've seen from the other samples in Deer's showroom.
The changes I'd make would be mainly aesthetic, but in terms of order process I would definitely have measurements taken in the morning while my feet haven't swollen up. I've noticed that in the morning the heel can be quite loose, but in the afternoon the fit is satisfactory. I'd rather have a tight initial fit that slowly loosens as I break the shoe in, than a heel that slips occasionally. My other stylistic changes I'd have to discuss with Rene to ascertain their possibility, but things like lacing options, seamless heel counters, and a double sole that tapers to a single sole in the waist of the shoe are things I'd like. Also, photos of the construction process would be very pleasing.