As you noted earlier, it is unfortunate that Panic isn’t here to speak for himself. Perhaps his stint in the office is almost over and he can rejoin the class soon.
One problem I have with Panic's theory is that the mixture has already been determined before it ever gets to the idle bleed.
According to the Armored School Handbook, the lowspeed mixture is determined by the needle, and the air orifice around it.
The angle of the disc cannot add fuel, it can only add air;
Air travels in the front hole to push emulsion out the rear hole.
The above is true only when the disc is totally or nearly closed. At nearly closed disc positions the idle slot acts as you describe - air enters the upstream side and air/fuel emulsion exits the downstream side. As disc opening progresses, i.e., the tip-in period, it reveals a continuum of different idle slot entry/exit ratios, and hence different air/fuel ratios. When the disc has moved sufficiently to reveal the entire idle slot, the slot becomes a constant source of fuel (fuel feeds from the entire slot length), rather than functioning as a mixing chamber, with air entering one end and emulsion exiting the other end of the slot, as it did at nearly closed disc positions.
So if Panic is correct that the mixture is changed, it would mean that low angles push less air in?
Or draw more emulsion out?
As described above, as the disc opens, the idle slot feeds more and more fuel for the reasons stated above. The disk angle determines the number of degrees of rotation that the disk interacts with the slot, and in turn the relative richness or leanness of the mixture emitted from the slot. Beveling a disc, e.g., an X-9 disc or altering the disc angle alters how the disc interacts with the slot, and hence the relative richness or leanness of the tip-in period.
If one decides to knife edge the leading edge of the disc, be aware that you will be altering the tip-in region for all the reasons mentioned above. However, knife edging the trailing edge is without consequence, so long as the outside disc dimension is not altered.