One suggestion I have if you are developing harsh edges is to not do the back and forth strokes but to only do one direction forward edge leading strokes. When you sharpen with spine leading or back strokes this can promote an exaggerated false or foil edge. A foil edge is just like a wire edge but it is not rolled up like a wire edge is.
In a basic sense, sharpening is creating friction between the stone and the steel. When we want to control the friction so it works for our benefit, the most effective change in the blade at the edge is accomplished by edge leading forward strokes. The back strokes-spine leading strokes do sharpen but not in a positive way and more haphazardly so we have less control over the outcome. Ask yourself, how much work would it be to hone a razor only with spine leading strokes? Think of it like driving a car going forward, when you put on the brakes the inertia of the car creates a nose dive of the front edge as the car deals with the friction of stopping. Now if you drive that same car in reverse and put on the brakes the back or rear end of the car (the spine in our case) dives down towards the pavement. This still stops the car but all of the energy was exerted on the back tires or our spine of the razor. We do not shave with the spine, only the front or edge.
For a straight razor blade as in the car above going in reverse, the spine recieves all of the benifit of the friction where it is lost as far as the cutting action is concerned. The front cutting edge is still engaged and is abrated to some degree but the steel is not altered or fashioned in a positive direct way. Sharpening is a task, a thoughful action to refine a blade using kinetic energy. It takes effort and we choose the media and the method to craft an edge so in this sense we should use all of that positive energy and direct it on the cutting edge and its formaiton. To me spine leading strokes are wasted energy and because their affect on the blade is minimal, the task performed by those strokes are the unknown or variable factor and are best eliminated unless you have a logical reason to perform them.
A stone is attempting to sharpening a razors edge from the first stroke, especially if the bevel is fully set all the way to the edge, and each stroke is a contributor to that goal which is to create is a geometrically sound edge shape. This edge shape is usually thought to be either wedge shaped or slightly convex shape. The convex shape adds more meat, thickness or body just behind the actual cutting edge thereby giving it strength and tenacity to hold up under the work of cutting hair. The weakest edge is a concave profile shape where the cutting edge protudes like a tongue out and away from the body of the blade and has less thickness behind the edge. Think of it graphically as the difference between a wedge type razor and a hollow ground razor. Which is stronger? A wedge shape edge is stronger than a hollow or concave type edge. In a concave shape the space between the actual edge and the thicker body of the blade, there is found to be a thinner area of steel. This gives the working edge a concave profile. This edge shape can appear to be very sharp at first but under a workload can break apart and become ragged and dull. This is a harsh edge.
Spine leading strokes promote these weak edges because when under abrasion circumstances. When energy is transfered from your hand through the steel and into the stone in the form of a kinetic forward/downward motion energy, the greater friction (abrasion) energies are delegated to the spine where it is wasted, while the minimal lesser portion of friction energies are relegatd to the following cutting edge. These lesser downward trailing energies encourage the formation of a very thin steel tongue at the cutting edge to remain intact because it just flops or folds back during sharpening instead of being honed off.
In razor honing or other fine steel edge creation there are always fragments of steel that flop at the edge of the blade because they are just moments or milimeters away from being abraded off, stroping can remove them. The higher quality steels with high carbon content usually have a finer granular make up, white paper steel is a good example. Alloy steels like blue paper steel have hard additives like cobalt which are usually larger particles and these add endurance to the blade. The fine high carbon steels will sharpen to a finer degree but because of their finer grain will promote a false edge or a burr and this is very thin, if you have finer abrasives to wear the burr or false edge of without breaking it off prematurely then I encourage this before stroping. Faint slurry mixes or just clear water can aid in removing by abrasion these fragile steel fragments that have very little structure holding them together before going to the strop.
Hope this helps,