I'm not sure having the bottom curve of the /a tangent to the vertical is what you want. You might want to move the control point to the left to let more light in. Conversely, you can try working with separate shapes for each element of the letter. This way you will have greater control over the pen logic of your design. The idea:
You can also just select the feature without any assignments, and the hyphen-minus sign before the feature tag disables it, e.g. "EB Garamond:-liga&dlig" disables standard ligatures and enables discretionary. That is a little bit more concise, but I find the ampersand the bottleneck: it would be so much easier to just type another colon.
Stinking buttons? I would even go for checkboxes, with the current state of affairs it is hardly possible to set features for arbitrarily chosen fragments of a passage of text and then change the font. And that's something I would like to do with my Blackletter design consisting of two layers, of which one is used for rubrication. If I want to customize the text to include ligatures and scribal abbreviations for some words and not for others (e.g. replicating a manuscript) and then copy the text and overlay the copy but only change the font to the rubrication font then LibO will erase all my work from the copy.
Okay, I know that's not something a lot of people need or care about... But still.
I even dare say some Poles can't tell the difference between a regular kreska and one slanted the opposite direction, like the grave accent. Especially in handwriting. Okay, maybe that sounded too blaming. As a matter of fact, since Polish doesn't use any grave accents, the direction doesn't really matter. So in handwriting, any stroke, vertical, diagonal - left or right, horizontal, makes for a legible kreska. It's not uncommon to see right slanted kreskas in rapid writing. It remains a fact that in print a more inclined kreska... Grzegorz Rolek said:
somehow feels spot on.
@Nick Shinn I don't feel qualified to answer that, but I recall seeing that kreska crossing the base letter many times. You might call it a traditional kludge, as it would often be used whenever the space is insufficient, possibly beside a strikethrough Ż (Z dot). I'm not quite sure however whether it's much of a cultivated tradition — such design brings to my mind old printing. Especially that ogoneks were also once (like in 1700s) straight strokes crossing the base letters.