Ah, you mean positioning the smaller parallel line (the BarMinHeight one) higher or lower, to simulate a perspective bar seen from different "altitude" angles, similar to a 3D model? Hmm... I doubt the OP had that kind of complexity in mind, but either way, this could in theory be achievable, but obviously it woud complicate a bit the implementation. It would also complicate your method of achieving this as well, because you'd have to similarly take into account that "altitude" / "altitude" angle (for both the frame / placeholder and the actual progress, see below).
In my samples, I assumed the most simple case, where the observer is at 0 degrees of altitude compared to the "vertical middle" of the frame / placeholder (like placing your eye at the vertical middle of a piece of paper that you place into perspective, i.e. rotate against the horizon plane, depending on which "wall" / "floor" you want it to be).
It's only the frame / placeholder (i.e. the green trapezoid in my samples) that is static, with its position, ratios, edge lengths staying the same. The actual progress shape (i.e. the red trapezoid in my samples) has the length of some of its edges / sides always fluctuating, based on what progress value it's representing. In my last code, for example, the "heights" (both the min and max) of the progress trapezoid are always changing (e.g. 0 when progress is 0%, half their original height when progress is 50% and so on). You can't set the path of such a trapezoid without using a formula that takes the progress value into account - that's the whole point of a progress "bar" (well, trapezoid in this case). A Bar meter would indeed spare the user of having to use a formula for this since it does the percentage computing in the background, but naturally due to the Bar meter's limitations in this specific case (e.g. you can't make it a trapezoid instead of a rectangle), you'd have to compute some stuff "manually".
That being said, it's true that my samples used only the "vertical progress bar" model. To be honest, I didn't realize it, but changing to a "horizontal progress bar" appearance shouldn't be that hard. It's a similar case of swapping some variables and formulas. Of course, I didn't yet quite get which "wall" the OP is talking about when positioning the perspective shape (nor the orientation, for that matter), so I just picked a random case (like the right wall and vertical progress bar orientation) to represent.