Stamina issues, hand placement and consistency

[Zyxel]

Yo I've been getting back into FFR after a long time but I'm running into an issue. As the title says, I have stamina issues which I imagine are a result of my hand placement. Most people do a 2-2 split with their hands (middle/index - index-middle), but I can't get my muscle memory or brain processes normal hand placement, and opt into using a 1-3 split.

I can comfortably FC charts between 70-90 difficulty, but certain patterns make playing incredibly difficult or even painful. This is my layout:

Left Hand: Index Finger (Tilde Key ~)
Right Hand: Index, Middle, Ring (J, I, O)

I currently struggle with consistency. My biggest issue is that certain patterns (namely Right-side trills with my middle and ring finger) are really hard and I can't get perfect accuracy. Certain patterns I physically cant do fast enough so my acc. prevents me from AAA'ing.

Any tips on developing higher stamina and consistency (without changing my key layout)?