Ok I slept on it (briefly), and also found these very helpful looking articles on shortening front rise and back rise. https://designerstitch.com/how-to-shorten-your-front-rise/ https://designerstitch.com/how-to-lengthen-your-back-rise/
The pictures in those look almost exactly like my issues, more than anything else I’ve found. So I feel validated in thinking I need a front rise shortened, and possibly a bit out of the back rise, and a bit added to crotch length at the inseam for full thigh to address those horizontal lines (added to front or back pattern piece? How different an effect will that have?)
Part of me would like to try darting out some of the crotch fullness by adding darts from the waist pointing down to where the thighs start. But at a certain extent I can’t, and shouldn’t be trying to, ‘fit out’ all the wrinkles/fullness at the front – some wearing ease is needed, and also the front of my thighs curve out beyond where my waist sits on the vertical access, so I would never be able to get the fabric to sit flat there as it travels out to that point. Even in my RTW skin tight stretch leggings, there are some wrinkles at the crotch-thigh meet points, I just checked.
Maybe too much of the waist circumference is distributed to the front pattern pieces, ie there is too much width in the front pattern pieces? Would the ideal fit actually be a smaller size but with a full seat/full thigh adjusment? I guess I need to make some trousers in a non-stretch, with the waistband as per the pattern, to test that one.
BUT it is exciting that I should be able to reduce some of that annoying baggy/low crotch fabric by reducing the rise. So I’ve basted out an inch wedge at CB from the back rise, and the 1.5″ wedge is still basted out of the front rise, and I’m going to wear them to work from home today and see how it settles. I may change the front basting to increase it to 2″, possibly change the angle, and attempt to shift the easing so it isn’t adding wrinkles, but we’ll see. [Ed. This post from Sasha at Secondo Piano makes me feel validated at taking a wedge out of front rise, although she is working on the back crotch, it does seem like the same issue: http://www.secondopiano.space/blog/2017/2/17/she-wears-the-pants-13%5D
If I’m right, and those alterations are good, I can’t help thinking I should be good and deconstruct the green velvet muslin and slash it to make those changes properly before constructing it back together. Will I be in a mood to bother?