You can get the expression selector movements to overlap if you decouple move time from the delay, like this maybe:
delay = 5; //number of frames to delay
dur = 7;
d0 = delay*thisComp.frameDuration*(textIndex-1);
ease(time,d0,d0+framesToTime(dur),100,0)
But yes, the technique appears to be clamped to the range from -100 to 100, so it’s only suitable for specific cases.