I just bought the IrPad 19mm normal size for my Go Big. The pads do not drop in, for they are a bit too small. Are the pads supposed to stretch to fit in? It does not seem like the pads will. Any ideas?
They ought be fit in quite snugly.
Yuki
You can try stretching them. Or as Yuki said they probably fit snug. 
They use standard sized 19mm YYJ silicone response pads.
They’ll fit, just work them in or silicone it.