I think I understand what do you mean - a photon is emitted on the side of the die. Then hits the collar. Then is reflected. Since it was off edge, it hits the die off another edge. When it’s re-emitted off edge AND is reemitted towards the open part of silicone - the chances of it reflecting off the silicone-air boundary are high.
If we managed to reflect it towards the centre of the die - it would have higher chances of escaping.
Yes, I think that near edge parts of the die have dead emission angles - where light TIRs off the air-silicone surface. I think that flat (or dedomed) emitters have these areas larger.
Yes, if we could redirect light towards the centre it would be better. Though it would also increase light loss at an earlier stage - light that bounces off collar but fails to hit the die.
I think that the optimal shape that maximises chances that a photon bounced off a collar would be near spherical.
I think that the optimal shape that maximises chances that a photon bounced off a collar eventually escapes the package is different. More light hits the collar from the closer end than from a farther therefore a flatter shape would probably be better.
Much flatter? I don’t know but I have a hunch that it’s not.
Anyway - we already have domes that are spherical or close to spherical. I believe their shape is imperfect but nevertheless good. I’m more worried about paints not sticking to the silicone or not surviving the heat….