Your picture shows why hi-cap .22 mags are typically curved.
I've been playing around with .22 mags a bit, this is what I've come up with. Reliable "straight" mags typically don't hold many more than 10 rounds. To feed properly into the chamber, you need to maintain pressure on the underside of the round, which keeps the round snug against the feed lips and feeds the round at the proper angle.
The problem arises with the rimmed case of the .22 (but this is no secret).
As you stack more rounds, your axis of the bottom round rotates so that the bullet faces more vertically. In the curved (butler creek style) mags, this isn't an issue as the follower maintains the same angle as the bottom round, which in turn maintains even pressure on the stack of rounds (front and back).
In a straight mag, the bottom round rotates its axis, but the follower doesn't change its angle and point of pressure. Once you get past a certain number of rounds stacked in this manner, you have upward pressure against the rim of the round stack, but none at the leading (business end). This is why straight mags of higher than 10 often misfeed, especially at full capacity. The nose of the top rounds are "floating" and not maintaining the correct feed angle. With enough rounds stacked, the top rounds will in fact sit in the mag "nose down."
This is just what I've learned from tearing different mags apart, building my own, and general experimenting. I'd love to have a 20-30 rd straight mag for my thompson 10/22, but in order for it to work, a follower would have to be developed that not only would adjust its angle to maintain front/back pressure on the entire stack of rounds, but would also have to lengthen itself as it went down, in order to fill the void that was created behind it as it rotates.
Does that make any sense? I've spent many hours in the shop trying to solve this problem, but the nature of the .22 shape dictates what works. An overall tapered shape leads to curved mags if you want capacity.
I'm rambling, and definitely not an expert on this.